Replace deprecated yield_fixture with fixture

Committed via https://github.com/asottile/all-repos
diff --git a/tests/forbid_new_submodules_test.py b/tests/forbid_new_submodules_test.py
index fb37862..dc64f06 100644
--- a/tests/forbid_new_submodules_test.py
+++ b/tests/forbid_new_submodules_test.py
@@ -6,7 +6,7 @@
 from pre_commit_hooks.forbid_new_submodules import main
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def git_dir_with_git_dir(tmpdir):
     with tmpdir.as_cwd():
         cmd_output('git', 'init', '.')