fix typo src/PIL/ImageGrab.py

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

src/PIL/ImageGrab.py

@@ -167,7 +167,7 @@ def grabclipboard():
             ]
             if any(e in err for e in allowed_errors):
                 return None
-            msg = f"{args[0]} error: {err.strip() if err else 'Unkown error'}"
+            msg = f"{args[0]} error: {err.strip() if err else 'Unknown error'}"
             raise ChildProcessError(msg)
 
         data = io.BytesIO(p.stdout)