chore: blacken (#375)

diff --git a/system_tests/test_default.py b/system_tests/test_default.py
index 23f6543..22213e6 100644
--- a/system_tests/test_default.py
+++ b/system_tests/test_default.py
@@ -16,7 +16,7 @@
 
 import google.auth
 
-EXPECT_PROJECT_ID = os.environ.get('EXPECT_PROJECT_ID')
+EXPECT_PROJECT_ID = os.environ.get("EXPECT_PROJECT_ID")
 
 
 def test_application_default_credentials(verify_refresh):