docs(get-images-from-files): document compose support (#28)

get-images-from-files already supports compose files. This PR explicitly documents the compatibility and includes a test.

Reviewed-on: t.behrendt/trivy-actions#28
Reviewed-by: branch-buddy <branch-buddy@t00n.de>
Co-authored-by: t.behrendt <t.behrendt@t00n.de>
Co-committed-by: t.behrendt <t.behrendt@t00n.de>

.gitea/workflows/ci.yaml

@@ -44,6 +44,7 @@ jobs:
           files: |
             - get-images-from-files/test.Dockerfile
             - get-images-from-files/test-deployment.yaml
+            - get-images-from-files/test-compose.yaml
       - name: Check image formats extracted
         run: |
           images="${{ steps.giff.outputs.images }}"
@@ -59,6 +60,10 @@ jobs:
           check "K8s registry+tag (app:v2)" "example.com/library/app:v2"
           check "K8s registry+digest (helper@sha256:...)" "example.com/myproject/helper@sha256:bbbbbbbb"
           
+          # Compose-only refs
+          check "Compose registry+tag (web:v3)" "example.com/compose/web:v3"
+          check "Compose registry+tag (worker:v3)" "example.com/compose/worker:v3"
+          
           # Shared ref (in both files) — must appear exactly once
           check "Shared ref present (distroless/static:nonroot)" "example.com/distroless/static:nonroot"
           count=$(echo "$images" | tr ',' '\n' | grep -c 'example.com/distroless/static:nonroot' || true)
@@ -66,7 +71,7 @@ jobs:
           [ "$count" -eq 1 ] && echo "OK (count=$count)" || { echo "FAIL (count=$count, expected 1)"; exit 1; }
           total=$(echo "$images" | tr ',' '\n' | grep -c . || true)
           echo -n "  Total unique refs: "
-          [ "$total" -eq 5 ] && echo "OK ($total)" || { echo "FAIL (got $total, expected 5)"; exit 1; }
+          [ "$total" -eq 7 ] && echo "OK ($total)" || { echo "FAIL (got $total, expected 7)"; exit 1; }
           
           echo ""
           echo "All checks passed."