tests: unset GIT_DIR after leaving bare repo context

Earlier commits in this series export `GIT_DIR` when entering
bare repositories. When the test subsequently leaves that
context via `cd`, the stale `GIT_DIR` must be cleaned up to
avoid confusing subsequent commands.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

t/t1400-update-ref.sh

@@ -32,7 +32,7 @@ test_expect_success setup '
 	cd $bare &&
 	git init --bare -b main &&
 	create_test_commits "bare" &&
-	cd -
+	cd - && sane_unset GIT_DIR
 '
 
 test_expect_success "create $m" '

t/t1800-hook.sh

@@ -535,7 +535,7 @@ test_expect_success 'server hooks expect stdout redirected to stderr' '
 	git remote add origin-server remote-server &&
 	cd remote-server &&
 	setup_hooks pre-receive update post-receive post-update &&
-	cd .. &&
+	cd .. && sane_unset GIT_DIR &&
 	git push origin-server HEAD:new-branch >stdout.actual 2>stderr.actual &&
 	check_stdout_merged_to_stderr pre-receive update post-receive post-update
 '

t/t2400-worktree-add.sh

@@ -219,7 +219,7 @@ test_expect_success '"add" to bare repo with worktree config' '
 		git config --worktree bogus.key value &&
 		git config --unset core.bare &&
 		git worktree add ../there4 main &&
-		cd ../there4 &&
+		cd ../there4 && sane_unset GIT_DIR &&
 
 		# Simple check that a Git command does not
 		# immediately fail with the current setup

t/t5500-fetch-pack.sh

@@ -458,7 +458,7 @@ test_expect_success 'fetch in shallow repo unreachable shallow objects' '
 		git tag -d TAGB1 TAGB2 &&
 		git update-ref refs/heads/B B~~ &&
 		git gc --prune=now &&
-		cd ../shallow9 &&
+		cd ../shallow9 && sane_unset GIT_DIR &&
 		git fetch origin &&
 		git fsck --no-dangling
 	)