Replace GH Action from tj-actions by custom code (openhab#18399)

The GitHub Actions build workflow includes external Actions from
3rd party repositories.
The functionality of tj-actions/verify-changed-files was used to
detect modifications of files during the build process.
The external action is removed and replaced by custom code.
This is less flexible, but does not require an external action in the
build toolchain.

Signed-off-by: Holger Friedrich <[email protected]>

Author: holgerfriedrich

.github/workflows/ci-build.yml

@@ -102,8 +102,11 @@ jobs:
           mode: inline
 
       - name: Verify Changed Files
-        uses: tj-actions/verify-changed-files@v20
         id: verify-changed-files
+        run: |
+          set -o pipefail
+          changed_files=$(echo -n "$(git diff --name-only HEAD && git ls-files --others --exclude-standard)"|tr '\n' ' ')
+          echo "changed_files=$changed_files" >> $GITHUB_OUTPUT
 
       - name: Fail on Changed Files
         if: steps.verify-changed-files.outputs.changed_files != ''