ci: workflow to build test snaps (#1460)

.github/workflows/snap.yml

@@ -0,0 +1,22 @@
+name: Build test Foliate Snap
+on:
+  push:
+    branches:
+      - gtk4
+  workflow_dispatch:
+
+jobs:
+  snap:
+    name: Build snap
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Change Source
+      run: yq 'del(.parts.foliate.source-tag) | .parts.foliate.source = "."' snapcraft.yaml
+    - uses: canonical/action-build@v1
+      id: snapcraft
+    - uses: actions/upload-artifact@v4
+      if: ${{ github.event_name == 'release' }} #uploads the snap only if it's a release
+      with:
+        name: amber-snap
+        path: ${{ steps.snapcraft.outputs.snap }}