Fix mypyc wheel tests

Author: cdce8p

mypyc/test/test_run.py

@@ -32,6 +32,7 @@
     assert_test_output,
     fudge_dir_mtimes,
     show_c,
+    test_data_prefix,
     use_custom_builtins,
 )
 
@@ -291,9 +292,7 @@ def run_case_step(self, testcase: DataDrivenTestCase, incremental_step: int) ->
             # No driver.py provided by test case. Use the default one
             # (mypyc/test-data/driver/driver.py) that calls each
             # function named test_*.
-            default_driver = os.path.join(
-                os.path.dirname(__file__), "..", "test-data", "driver", "driver.py"
-            )
+            default_driver = os.path.join(test_data_prefix, "driver", "driver.py")
             shutil.copy(default_driver, driver_path)
         env = os.environ.copy()
         env["MYPYC_RUN_BENCH"] = "1" if bench else "0"