[CI] Adopt GitHub actions

# Motivation

We want to migrate all of repositories to use GitHub Actions.

# Modification

This PR adopts GH actions in this repo.

# Result

New and shiny CI.

.github/workflows/main.yml

@@ -0,0 +1,20 @@
+name: Main
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  unit-tests:
+    name: Unit tests
+    uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+    with:
+      linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_nightly_6_0_arguments_override: "--explicit-target-dependency-import-check error"
+      linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error"
+
+  cxx-interop:
+    name: Cxx interop
+    uses: apple/swift-nio/.github/workflows/cxx_interop.yml@main

.github/workflows/pull_request.yml

@@ -0,0 +1,33 @@
+name: PR
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize]
+
+jobs:
+  soundness:
+    name: Soundness
+    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    with:
+      license_header_check_project_name: "SwiftCrypto"
+
+  cmake-lists:
+    name: Check cmake lists
+    uses: apple/swift-nio/.github/workflows/swift_matrix.yml@main
+    with:
+      name: "Check cmake lists"
+      matrix_linux_command: ./scripts/check-cmake-lists.sh
+
+  unit-tests:
+    name: Unit tests
+    uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+    with:
+      linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_nightly_6_0_arguments_override: "--explicit-target-dependency-import-check error"
+      linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error"
+
+  cxx-interop:
+    name: Cxx interop
+    uses: apple/swift-nio/.github/workflows/cxx_interop.yml@main

.github/workflows/pull_request_label.yml

@@ -0,0 +1,18 @@
+name: PR label
+
+on:
+  pull_request:
+    types: [labeled, unlabeled, opened, reopened, synchronize]
+
+jobs:
+  semver-label-check:
+    name: Semantic Version label check
+    runs-on: ubuntu-latest
+    timeout-minutes: 1
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: Check for Semantic Version label
+        uses: apple/swift-nio/.github/actions/pull_request_semver_label_checker@main

.github/workflows/scheduled.yml

@@ -0,0 +1,20 @@
+name: Scheduled
+
+on:
+  schedule:
+    - cron: "0 8,20 * * *"
+
+jobs:
+  unit-tests:
+    name: Unit tests
+    uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+    with:
+      linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+      linux_nightly_6_0_arguments_override: "--explicit-target-dependency-import-check error"
+      linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error"
+
+  cxx-interop:
+    name: Cxx interop
+    uses: apple/swift-nio/.github/workflows/cxx_interop.yml@main

scripts/check-cmake-lists.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftCertificates open source project
+##
+## Copyright (c) 2024 Apple Inc. and the SwiftCertificates project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of SwiftCertificates project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+set -euo pipefail
+
+log() { printf -- "** %s\n" "$*" >&2; }
+error() { printf -- "** ERROR: %s\n" "$*" >&2; }
+fatal() { error "$@"; exit 1; }
+
+log "Checking if the cmake files are up-to-date..."
+
+here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+FIRST_OUT="$(git status --porcelain)"
+_=$("$here"/update-cmake-lists.sh 2>&1)
+SECOND_OUT="$(git status --porcelain)"
+if [[ "$FIRST_OUT" != "$SECOND_OUT" ]]; then
+  error "Changes in the cmake files detected. Please run the update-cmake-lists.sh script."
+  exit 1
+fi
+
+log "✅ cmake files are up-to-date."