scripts: fetch branch before checkout in release script

actions/checkout does a sparse clone by default so the branch may not
be yet available.

Reviewed-by: Justin Stephenson <jstephen@redhat.com>

Author: pbrezina

scripts/release.sh

@@ -62,6 +62,7 @@ GROUP_END
 set -x
 
 GROUP_START "Checkout branch"
+git fetch origin "$branch"
 git checkout "$branch"
 git pull --rebase
 GROUP_END