fix(examples): fix YAML syntax error for MAINTAINERS environment variable fallback

Author: cocosheng-g

examples/workflows/issue-cleanup/gemini-issue-cleanup.yml

@@ -71,7 +71,7 @@ jobs:
         uses: 'actions/github-script@v7'
         env:
           ISSUE_NUMBER: '${{ matrix.issue_number }}'
-          MAINTAINERS: "${{ inputs.maintainers || vars.MAINTAINERS || ' }}"
+          MAINTAINERS: '${{ inputs.maintainers || vars.MAINTAINERS }}'
         with:
           script: |-
             const issueNumber = parseInt(process.env.ISSUE_NUMBER, 10);