Add a comment about 'type: ignore' for WindowsFlag

Author: dlax

pylsp_mypy/plugin.py

@@ -64,7 +64,7 @@
 # Windows started opening opening a cmd-like window for every subprocess call
 # This flag prevents that.
 # This flag is new in python 3.7
-# This flag only exists on Windows
+# This flag only exists on Windows, hence the 'type: ignore[attr-defined]' below.
 class WindowsFlag(TypedDict, total=False):
     creationflags: int