build: try to fix fast-forward workflow

.github/workflows/fast_forward.yml

@@ -52,8 +52,8 @@ jobs:
 
       - name: Set environment variables
         run: |
-          MERGE_STATUS=${{ fromJson(steps.get-pr-details.outputs.data).mergeable_state }}
-          if [ "$MERGE_STATUS" != "clean" ]; then echo "COMMENT=[Fast Forward CI] ${{ env.HEAD_REF }} cannot be merged into ${{ env.BASE_REF }} at the moment." >> $GITHUB_ENV; fi
+          MERGE_STATUS=${{ fromJson(steps.get-pr-details.outputs.data).mergeable }}
+          if [ "$MERGE_STATUS" != "true" ]; then echo "COMMENT=[Fast Forward CI] ${{ env.HEAD_REF }} cannot be merged into ${{ env.BASE_REF }} at the moment." >> $GITHUB_ENV; fi
           echo "MERGE_STATUS=$MERGE_STATUS" >> $GITHUB_ENV
           echo "BASE_REF=${{ fromJson(steps.get-pr-details.outputs.data).base.ref }}" >> $GITHUB_ENV
           echo "HEAD_REF=${{ fromJson(steps.get-pr-details.outputs.data).head.ref }}" >> $GITHUB_ENV
@@ -62,7 +62,7 @@ jobs:
       # Only runs if the merge status is "clean", clean might refer to when the merge button is green in the PR's page, there's no clear indication of it's values in docs
       # For forks the following script adds the fork as a remote, them merges it into base
       - name: Merge the head branch into base in a fast forward manner only
-        if: ${{ env.MERGE_STATUS == 'clean' }}
+        if: ${{ env.MERGE_STATUS == 'true' }}
         run: |
           git config --global user.email "[email protected]"
           git config --global user.name "GitHub Action"