build: ensure only one PR commit message comment gets created

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: na
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: na
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: na
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: na
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: Planeshifter

.github/workflows/generate_pr_commit_message.yml

@@ -82,13 +82,23 @@ jobs:
           # Ensure the script itself doesn't fail the workflow:
           exit 0
 
+      # Check if the commit message already exists in the PR comments:
+      - name: 'Check if commit message already exists in PR comments'
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e # v3.1.0
+        id: fc
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          body-includes: '<!-- PR_COMMIT_MESSAGE -->'
+
       # Post commit message as PR comment:
       - name: 'Post commit message as PR comment'
         # Pin action to full length commit SHA
         uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043 # v4.0.0
         with:
           token: ${{ secrets.STDLIB_BOT_PAT_REPO_WRITE }}
+          comment-id: ${{ steps.fc.outputs.comment-id }}
           issue-number: ${{ github.event.pull_request.number }}
+          edit-mode: replace
           body: |
             ### PR Commit Message