Merge branch 'tc/show-ref-exists-fix' into maint-2.43

Update to a new feature recently added, "git show-ref --exists".

* tc/show-ref-exists-fix:
  builtin/show-ref: treat directory as non-existing in --exists

diff --cc builtin/show-ref.c
Simple merge

diff --cc t/t1403-show-ref.sh
Simple merge