Drop a stale type-ignore in test_rust_dbapi

`Cursor.fetchone` is annotated `-> Any` on this branch, so mypy flags the
ignore as unused and CI's lint would fail.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019ZdvuLkg7Lm7wDtPQzDnJx

tests/storage/test_rust_dbapi.py

@@ -336,7 +336,7 @@ class RustDBAPIAdapterTestCase(unittest.TestCase):
         def backend_pid(conn: rust_dbapi.Connection) -> int:
             cursor = conn.cursor()
             cursor.execute("SELECT pg_backend_pid()")
-            (pid,) = cursor.fetchone()  # type: ignore[misc]
+            (pid,) = cursor.fetchone()
             conn.commit()
             return pid