Rollup merge of rust-lang#149605 - Kobzol:unshalllow-beta, r=cuviper

Use branch name instead of HEAD when unshallowing

Fixes a regression with the beta channel that was discovered in rust-lang#149572.

r? `@cuviper`

Author: matthiaskrgr

src/ci/scripts/checkout-submodules.sh

@@ -17,7 +17,7 @@ ci_dir=$(cd $(dirname $0) && pwd)/..
 # On the beta channel we'll be automatically calculating the prerelease version
 # via the git history, so unshallow our shallow clone from CI.
 if [ "$(releaseChannel)" = "beta" ]; then
-  git fetch origin --unshallow beta HEAD
+  git fetch origin --unshallow beta main
 fi
 
 function fetch_github_commit_archive {