try this one?

.github/workflows/shellcheck.yml

@@ -1,18 +1,16 @@
 # from here: https://github.com/marketplace/actions/shellcheck
-- name: ShellCheck
-  # You may pin to the exact commit or the version.
-  # uses: ludeeus/action-shellcheck@d586102c117f97e63d7e3b56629d269efc9a7c60
-  uses: ludeeus/action-shellcheck@1.0.0
-#  with:
-#    # A space seperated list of additional filename to check
-#    additional_files: # optional, default is 
-#    # Paths to ignore when running ShellCheck
-#    ignore: # optional, default is 
-#    # Minimum severity of errors to consider. Options: [error, warning, info, style]
-#    severity: # optional, default is 
-#    # Run shellcheck on _all_ files at once, instead of one at a time
-#    check_together: # optional, default is 
-#    # Directory to be searched for files. Defaults to .
-#    scandir: # optional, default is .
-#    # Set to true to skip using problem-matcher
-#    disable_matcher: # optional, default is false
+on:
+  push:
+    branch:
+      - master
+
+name: 'Trigger: Push action'
+
+jobs:
+  shellcheck:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Run ShellCheck
+      uses: ludeeus/action-shellcheck@master