t5509: use a bare repository for test push target

`receive.denyCurrentBranch` currently has a bug where it allows pushing
into non-bare repository using namespaces as long as it does not have any
commits. This would cause t5509 to fail once that bug is fixed because it
pushes into an unborn current branch.

In t5509, no operations are performed inside `pushee`, as it is only a
target for `git push` and `git ls-remote` calls. Therefore it does not
need to have a worktree. So, it is safe to change `pushee` to a bare
repository.

Helped-by: Johannes Schindelin <[email protected]>
Signed-off-by: Hariom Verma <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: harry-hov

t/t5509-fetch-push-namespaces.sh

@@ -20,7 +20,7 @@ test_expect_success setup '
 	) &&
 	commit0=$(cd original && git rev-parse HEAD^) &&
 	commit1=$(cd original && git rev-parse HEAD) &&
-	git init pushee &&
+	git init --bare pushee &&
 	git init puller
 '