ci: Make sure git knows the main branch

Something seems to have changed about how sparse checkouts are done on GHA, so the main branch isn't found.

(cherry picked from commit 184a242937)

.github/workflows/release.yml

@@ -110,6 +110,7 @@ jobs:
       - name: Cherry-pick release commit
         if: ${{ inputs.release_type == 'patch' }}
         run: |
+            git fetch origin main
             git checkout main
             git cherry-pick -x v${{ steps.bump.outputs.version }}
             git push origin main