🧪💅 Describe free-threading workflow input

Previously, it didn't have a human-readable explanation which is a
bad tone as it's less obvious how it's supposed to be used.

Author: webknjaz

.github/workflows/reusable-windows.yml

@@ -2,6 +2,7 @@ on:
   workflow_call:
     inputs:
       free-threading:
+        description: Whether to use no-GIL mode
         required: false
         type: boolean
         default: false