Try to fix logic

.github/workflows/mega-linter.yml

@@ -54,7 +54,7 @@ jobs:
           # https://megalinter.io/configuration/
           # Validates all source when push on main, else just the git diff with main.
           # Override with true if you always want to lint all sources
-          VALIDATE_ALL_CODEBASE: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
+          VALIDATE_ALL_CODEBASE: ${{ ((github.event_name == 'push' && github.ref == 'refs/heads/main') && 'true') || 'false' }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           # ADD YOUR CUSTOM ENV VARIABLES HERE OR DEFINE THEM IN A FILE .mega-linter.yml AT THE ROOT OF YOUR REPOSITORY
           DISABLE: COPYPASTE