Re-use windows_flag in test

Author: dlax

test/test_plugin.py

@@ -30,10 +30,6 @@
     'test_plugin.py:124:1:129:77: note: Use "-> None" if function does not return a value'
 )
 
-windows_flag: dict[str, int] = (
-    {"creationflags": subprocess.CREATE_NO_WINDOW} if os.name == "nt" else {}  # type: ignore
-)
-
 
 @pytest.fixture
 def last_diagnostics_monkeypatch(monkeypatch):
@@ -251,7 +247,7 @@ def test_option_overrides_dmypy(last_diagnostics_monkeypatch, workspace):
         "--no-pretty",
         document.path,
     ]
-    m.assert_called_with(expected, capture_output=True, **windows_flag, encoding="utf-8")
+    m.assert_called_with(expected, capture_output=True, **plugin.windows_flag, encoding="utf-8")
 
 
 def test_dmypy_status_file(tmpdir, last_diagnostics_monkeypatch, workspace):