[v11.0.x] CI: use main instead of my branch in release-pr.yml (#91006)

CI: use main instead of my branch in release-pr.yml (#91004)

use main instead of my branch

(cherry picked from commit 7e4b7f73e7)

Co-authored-by: Kevin Minehart <5140827+kminehart@users.noreply.github.com>
(cherry picked from commit a779d2bc81)

.github/workflows/release-pr.yml

@@ -65,7 +65,7 @@ jobs:
       - name: Checkout Grafana (main)
         uses: actions/checkout@v4
         with:
-          ref: km/fix-release-pr-target
+          ref: main
           fetch-depth: '0'
           fetch-tags: 'false'
           path: .grafana-main