fix(ci): diff_check action should succeed on non-PR runs (#3742)

* fix(ci): `diff_check` action should succeed on non-PR runs

* test skipped steps

* Revert "test skipped steps"

This reverts commit ec059dd.

.github/workflows/skip-ci.yml

@@ -14,25 +14,33 @@ jobs:
       skip_ci:
         ${{ steps.check_diff.outputs.skip_ci }}
     steps:
+      - name: Check if is PR
+        id: check-pr
+        run: |
+          if [ -z "${{ github.event.pull_request.number }}" ] || [ -z "${{ github.base_ref }}" ] || [ -z "${{ github.head_ref }}" ]; then
+            echo "This action is intended to be run on pull requests only."
+            echo "is-pr=false" >> $GITHUB_OUTPUT
+          else
+            echo "is-pr=true" >> $GITHUB_OUTPUT
+          fi
+
       - name: Checkout PR Base Branch
+        if: steps.check-pr.outputs.is-pr == 'true'
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
           ref: ${{ github.base_ref }}
 
       - name: Checkout PR Head Branch
+        if: steps.check-pr.outputs.is-pr == 'true'
         run: |
           git fetch origin pull/${{ github.event.pull_request.number }}/head:${{ github.head_ref }}
           git checkout ${{ github.head_ref }}
 
       - name: Check diff from Pull Request
+        if: steps.check-pr.outputs.is-pr == 'true'
         id: check_diff
         run: |
-          if [ -z "${{ github.base_ref }}" ] || [ -z "${{ github.head_ref }}" ]; then
-            echo "This action is intended to be run on pull requests only."
-            exit 0
-          fi
-
           skipList=(".github/CODEOWNERS" ".prettierignore")
           # Ignores changelog.md, readme.md,...
           fileChangesArray=($(git diff --name-only ${{ github.base_ref }}...${{ github.head_ref }} | grep -v '\.md$' || true))