build-test-recipe.yml: fix getting changed recipes from a fork

.github/workflows/build-test-recipe.yml

@@ -15,17 +15,34 @@ jobs:
     - name: Diff files and set variables
       id: diff
       run: |
-        # See https://github.community/t/check-pushed-file-changes-with-git-diff-tree-in-github-actions/17220/10
         if [ $GITHUB_BASE_REF ]; then
           # Pull Request
-          # 'github.event.before/after' and 'github.event.pull_request.base.sha' are inconsistent for PRs
-          # Find the commit where the PR branch was forked from the base branch
-          git fetch origin ${{ github.base_ref }} ${{ github.event.pull_request.head.ref }}
-          FORK_POINT=$( git show-branch --merge-base "origin/${{ github.base_ref }}" "origin/${{ github.event.pull_request.head.ref }}" )
+          # Fetch the base ref
+          git fetch origin ${{ github.base_ref }}:${{ github.base_ref }}
+
+          # For forks, we need to fetch from the head repository
+          if [ "${{ github.event.pull_request.head.repo.full_name }}" != "${{ github.repository }}" ]; then
+            git remote add fork ${{ github.event.pull_request.head.repo.clone_url }}
+            git fetch fork ${{ github.head_ref }}
+          else
+            git fetch origin ${{ github.head_ref }}:${{ github.head_ref }}
+          fi
+
+          # Determine the merge base
+          FORK_POINT=$(git merge-base ${{ github.base_ref }} ${{ github.event.pull_request.head.sha }})
           LATEST_COMMIT_IN_PR=${{ github.event.pull_request.head.sha }}
-          export DIFF=$( git diff --name-only $FORK_POINT $LATEST_COMMIT_IN_PR )
+
+          # Get the diff
+          DIFF=$(git diff --name-only $FORK_POINT $LATEST_COMMIT_IN_PR)
           echo "Diff between $FORK_POINT and $LATEST_COMMIT_IN_PR"
+        else
+          # Push to a branch
+          BEFORE_SHA=${{ github.event.before }}
+          AFTER_SHA=${{ github.event.after }}
+          DIFF=$(git diff --name-only $BEFORE_SHA $AFTER_SHA)
+          echo "Diff between $BEFORE_SHA and $AFTER_SHA"
         fi
+
         echo "$DIFF"
         echo "diff=$( echo "$DIFF" | tr '\n' ' ' )" >> $GITHUB_OUTPUT
     - name: Get Yocto release name