added "/" to the stub file to indicate that the first arg is positional only

Author: XFajk

buildconfig/stubs/pygame/geometry.pyi

@@ -198,5 +198,5 @@ class Line:
     def flip_ab(self) -> Line: ...
     def flip_ab_ip(self) -> None: ...
     def project(
-        self, point: tuple[float, float], clamp: bool = False
+        self, point: tuple[float, float], / clamp: bool = False
     ) -> tuple[float, float]: ...