cmd/update-reset: use stable tag.

Currently we always reset Homebrew/brew onto the latest `master`.
Instead, let's correctly use the latest tag when appropriate.

Library/Homebrew/cmd/update-reset.sh

@@ -75,9 +75,21 @@ homebrew-update-reset() {
  echo
 
  ohai "Resetting ${DIR}..."
- head="$(git -C "${DIR}" symbolic-ref refs/remotes/origin/HEAD)"
- head="${head#refs/remotes/origin/}"
- git -C "${DIR}" checkout --force -B "${head}" origin/HEAD
+ # HOMEBREW_* variables here may all set by bin/brew or the user
+ # shellcheck disable=SC2154
+ if [[ "${DIR}" == "${HOMEBREW_REPOSITORY}" &&
+ (-n "${HOMEBREW_UPDATE_TO_TAG}" ||
+ (-z "${HOMEBREW_DEVELOPER}" && -z "${HOMEBREW_DEV_CMD_RUN}")) ]]
+ then
+ local latest_git_tag
+ latest_git_tag="$(git -C "${DIR}" tag --list --sort="-version:refname" | head -n1)"
+
+ git -C "${DIR}" checkout --force -B stable "${latest_git_tag}"
+ else
+ head="$(git -C "${DIR}" symbolic-ref refs/remotes/origin/HEAD)"
+ head="${head#refs/remotes/origin/}"
+ git -C "${DIR}" checkout --force -B "${head}" origin/HEAD
+ fi
  echo
  done
 }