.github: Lint modified files only with Super-Linter (apache#6531)

https://github.com/github/super-linter#standard-image

Author: jbampton

.github/workflows/linter.yml

@@ -30,9 +30,15 @@ jobs:
     name: SuperLinter Check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - name: Checkout Code
+        uses: actions/checkout@v3
+        with:
+          # Full git history is needed to get a proper list of changed files within `super-linter`
+          fetch-depth: 0
       - name: SuperLinter
         uses: github/super-linter@v4
         env:
-          VALIDATE_PYTHON_FLAKE8: true
+          DEFAULT_BRANCH: main
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          VALIDATE_ALL_CODEBASE: false
+          VALIDATE_PYTHON_FLAKE8: true