Add shellcheck action to CI

.github/workflows/main.yaml

@@ -23,6 +23,11 @@ jobs:
         cd ../../
         PREFIX="$PREFIX" make test-ci
         cat junit.xml
+    - name: Run ShellCheck
+      uses: ludeeus/action-shellcheck@master
+      with:
+        ignore_paths: deps tests installed
+        scandir: .
     - name: Publish Test Report
       uses: mikepenz/action-junit-report@v5
       if: success() || failure() # always run even if the previous step fails