chore(ci): pin setup-python to truthful version comment

The pinned commit a309ff8 for actions/setup-python resolves to release
tag v6.2.0, but the inline comment claimed `# v6` (the floating major
tag, which points at a different commit). zizmor's ref-version-mismatch
rule flags this mismatch because the comment misrepresents the exact
pinned version. Updated both occurrences to `# v6.2.0` so the comment
matches the pinned SHA.

Resolves code-scanning alert #2549

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/actions/setup-backend/action.yml

@@ -42,7 +42,7 @@ runs:
         fi
         echo "python-version=$RESOLVED_VERSION" >> "$GITHUB_OUTPUT"
     - name: Set up Python ${{ steps.set-python-version.outputs.python-version }}
-      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
+      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
       with:
         python-version: ${{ steps.set-python-version.outputs.python-version }}
         cache: ${{ inputs.cache }}

.github/workflows/bump-python-package.yml

@@ -40,7 +40,7 @@ jobs:
         uses: ./.github/actions/setup-supersetbot/
 
       - name: Set up Python ${{ inputs.python-version }}
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: "3.10"