repo: Use the worktree when checking the repo rev.

Avoids treating the operation as if it were acting on a bare repository, thereby triggering failures when the Git client is configured with `safe.bareRepository=explicit`. Repo doesn't actually use a bare repository, but pointing at the gitdir acts as if it had.

Bug: 307559774
Change-Id: I2c142275b2726a59526729c0b2c54faf728f125d
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/391554
Commit-Queue: Jason R. Coombs <jaraco@google.com>
Tested-by: Jason R. Coombs <jaraco@google.com>
Tested-by: Emily Shaffer <emilyshaffer@google.com>
Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
diff --git a/subcmds/init.py b/subcmds/init.py
index 4451787..e53d033 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -353,7 +353,7 @@
             wrapper = Wrapper()
             try:
                 remote_ref, rev = wrapper.check_repo_rev(
-                    rp.gitdir,
+                    rp.worktree,
                     opt.repo_rev,
                     repo_verify=opt.repo_verify,
                     quiet=opt.quiet,