Update containers.build.yaml

Signed-off-by: Kjeld Schouten <info@kjeldschouten.nl>

.github/workflows/containers.build.yaml

@@ -29,6 +29,7 @@ jobs:
     runs-on: ubuntu-24.04
     outputs:
       matrix: '{"container": ${{ steps.reduce.outputs.containers }} }'
+      containers_found: ${{ steps.reduce.outputs.containers_found }} # New output
     steps:
       - name: Checkout
         uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4
@@ -45,7 +46,16 @@ jobs:
       - id: reduce
         run: |
           CONTAINERS=$(jq --raw-output '.changed_files | fromjson | .[] |= sub("(?<filepath>/?containers/(?<first_directory>(?<root1>[/]?)[^/]+/)(?<second_directory>(?<root2>[/]?)[^/]+)(?<extra_paths>/[^/]+)*)"; "\(.second_directory)") | unique' changes.json)
+          
+          # Set the containers output
           echo ::set-output name=containers::${CONTAINERS}
+          
+          # Check if containers were found and set the containers_found output
+          if [[ -z "$CONTAINERS" ]]; then
+            echo ::set-output name=containers_found::false
+          else
+            echo ::set-output name=containers_found::true
+          fi
 
   hadolint:
     name: Run hadolint
@@ -85,7 +95,7 @@ jobs:
     strategy:
       matrix: ${{ fromJson(needs.changes.outputs.matrix) }}
       fail-fast: false
-    if: ${{ needs.changes.outputs.matrix != '{}' && needs.changes.outputs.matrix != '' &&  fromJson(needs.changes.outputs.matrix).container != null }}
+    if: ${{ needs.changes.outputs.containers_found == 'true' }}
     steps:
       - name: Checkout
         uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4