ci: Add revdep-ci for bootc

This ensures when composefs changes, we don't break bootc.
This test isn't too expensive and should be reliable, so
I'm hopeful we can just enable it on every PR.

ref: #336

.dockerignore

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+target

.github/workflows/ci-bootc.yml

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+name: revdep CI bootc
+
+permissions:
+  actions: read
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch: {}
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  c9s-bootc-e2e:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+      - name: build
+        run: sudo podman build -t localhost/test:latest -f ci/Containerfile.c9s-bootc .
+      - name: bootc install
+        run: |
+          set -xeuo pipefail
+          sudo podman run --env BOOTC_SKIP_SELINUX_HOST_CHECK=1 --rm -ti --privileged -v /:/target --pid=host --security-opt label=disable \
+            -v /dev:/dev -v /var/lib/containers:/var/lib/containers \
+            localhost/test:latest bootc install to-filesystem --skip-fetch-check \
+             --replace=alongside /target

ci/Containerfile.c9s-bootc

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+FROM quay.io/centos/centos:stream9 as build
+RUN dnf -y install dnf-utils zstd && dnf config-manager --enable crb && dnf builddep -y composefs && \
+    dnf -y install meson
+COPY . /build
+WORKDIR /build
+RUN set -x; ls -al; meson setup target --prefix=/usr && meson compile -C target && \
+    env DESTDIR=$(pwd)/target/instroot meson install -C target
+
+FROM quay.io/centos-bootc/centos-bootc-dev:stream9
+COPY --from=build /build/target/instroot/usr/ /usr/