ci: Add "CI" GitHub Actions workflow

Author: hebasto

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+name: CI
+on: [pull_request, push]
+
+jobs:
+  modified_files:
+    runs-on: ubuntu-latest
+    outputs:
+      all: ${{ steps.changes.outputs.modified_files}}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Get modified files
+        id: changes
+        env:
+          COMMIT_BEFORE: ${{ github.event_name != 'pull_request' && github.event.pull_request.base.sha || (github.event.before != '0000000000000000000000000000000000000000' && github.event.before || github.event.repository.default_branch) }}
+        run: |
+          git fetch --depth=1 origin "$COMMIT_BEFORE"
+          echo "modified_files=$(git diff --name-only FETCH_HEAD ${{ github.sha }} | xargs)" >> "$GITHUB_OUTPUT"
+
+  docker_image:
+    uses: ./.github/workflows/docker.yml
+    permissions:
+      packages: write
+    needs: modified_files
+    if: contains(needs.modified_files.outputs.all, '.github/workflows/docker.yml') || contains(needs.modified_files.outputs.all, 'ci/linux-debian.Dockerfile')