Add yamllint, fix most yaml errors

.github/dependabot.yml

@@ -1,3 +1,4 @@
+---
 version: 2
 updates:
   - package-ecosystem: "github-actions"

.github/workflows/ci.yml

@@ -1,3 +1,4 @@
+---
 name: "CI"
 on:
   push:
@@ -37,7 +38,9 @@ jobs:
   build-test:
     name: Build and Test
     runs-on: ubuntu-20.04
-    needs: [ "lint", "shellcheck" ]
+    needs:
+      - lint
+      - shellcheck
     steps:
       - uses: actions/checkout@v3
       - name: Build Docker image
@@ -55,7 +58,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - name: Run integration test 1
+      - name: Run integration test 1 - good Dockerfile
         uses: ./
         with:
           dockerfile: testdata/Dockerfile
@@ -117,6 +120,15 @@ jobs:
       #    format: sarif
       #    output-file: report.sarif
 
+      - name: Run integration test 9 - run with no Dockerfiles
+        # This should not fail if no Dockerfiles are found in the path
+        # especially if git change deletes Dockerfile
+        uses: testdata/test_empty_dir
+        with:
+          dockerfile: ""
+          failure-threshold: error
+          recursive: true
+
   release:
     if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     name: Release

.pre-commit-config.yaml

@@ -1,3 +1,5 @@
+---
+repos:
   - repo: local
     hooks:
       - id: lint-dockerfile
@@ -5,8 +7,17 @@
         entry: make lint-dockerfile
         language: system
         files: \.yml$
+
       - id: lint-yaml
         name: Lint YAML
         entry: make lint-yaml
         language: system
         files: \.yml$
+  - repo: https://github.com/adrienverge/yamllint
+    rev: v1.33.0
+    hooks:
+      - id: yamllint
+  - repo: https://github.com/koalaman/shellcheck-precommit
+    rev: v0.9.0
+    hooks:
+      - id: shellcheck

.yamllint.yaml

@@ -6,3 +6,5 @@ rules:
     max: 80
     level: warning
   document-start: disable
+  truthy:
+    level: warning