ci: change workflow if statement syntax

.github/workflows/reject-pr.yaml

@@ -50,7 +50,7 @@ jobs:
             exit 1
           fi
       - name: Block commits made using the GitHub WebUI
-        if: steps.check_committer.outputs.committer_gitweb == "true"
+        if: steps.check_committer.outputs.committer_gitweb == 'true'
         uses: peter-evans/close-pull@v3
         with:
           # yamllint disable-line rule:line-length