cherry-pick: fetch full history so release branches are visible

actions/checkout@v4 defaults to fetch-depth: 1, so
`git branch -r | grep release` in hack/scripts/cherry-pick.sh
returned nothing and the loop body never executed.

Author: tamalsaha

.github/workflows/cherry-pick.yml

@@ -11,6 +11,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        with:
+          fetch-depth: 0
 
       - name: Generate LGTM App token
         id: lgtm-app-token