Swap external action to verify changed files for inline code

In the light of recent security issues, we are choosing to use our own
code to replace an external action.

See
https://www.stepsecurity.io/blog/harden-runner-detection-tj-actions-changed-files-action-is-compromised
for context

Author: rlazo

.github/workflows/release-note-changes.yml

@@ -6,7 +6,7 @@ on:
       - 'main'
 
 jobs:
-  build:
+  release-notes-changed:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/[email protected]
@@ -18,12 +18,16 @@ jobs:
 
       - name: Get changed changelog files
         id: changed-files
-        uses: tj-actions/[email protected]
-        with:
-          files_ignore: |
-            plugins/**
-          files: |
-            **/CHANGELOG.md
+        run: |
+          git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha}} | grep CHANGELOG.md > /tmp/changelog_file_list.txt
+          if [[ "$?" == "0" ]]
+          then
+            echo "any_changed=true" >> $GITHUB_OUTPUT
+          else
+            echo "any_changed=false" >> $GITHUB_OUTPUT
+          fi
+          echo "all_changed_files=$(cat /tmp/changelog_file_list.txt)" >> $GITHUB_OUTPUT
+          rm /tmp/changelog_file_list.txt
 
       - name: Set up JDK 17
         uses: actions/[email protected]