python: Replace universal_newlines with text.

This is supported in Python ≥ 3.7.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/test_fixtures.py

@@ -370,7 +370,7 @@ def destroy_leaked_test_databases(expiry_time: int = 60 * 60) -> int:
         ["psql", "-q", "-v", "ON_ERROR_STOP=1", "-h", "localhost", "postgres", "zulip_test"],
         input=commands,
         check=True,
-        universal_newlines=True,
+        text=True,
     )
     return len(databases_to_drop)