minor typing fixes (#2110)

Author: nfearnley

arcade/gl/context.py

@@ -407,7 +407,7 @@ def activate(cls, ctx: "Context"):
         """
         cls.active = ctx
 
-    def enable(self, *flags):
+    def enable(self, *flags: int):
         """
         Enables one or more context flags::
 
@@ -421,7 +421,7 @@ def enable(self, *flags):
         for flag in flags:
             gl.glEnable(flag)
 
-    def enable_only(self, *args):
+    def enable_only(self, *args: int):
         """
         Enable only some flags. This will disable all other flags.
         This is a simple way to ensure that context flag states

arcade/gl/vertex_array.py

@@ -138,7 +138,7 @@ def delete_glo(ctx: "Context", glo: gl.GLuint):
         ctx.stats.decr("vertex_array")
 
     def _build(
-        self, program: Program, content: Sequence[BufferDescription], index_buffer
+        self, program: Program, content: Sequence[BufferDescription], index_buffer: Optional[Buffer]
     ):
         """Build a vertex array compatible with the program passed in"""
         gl.glGenVertexArrays(1, byref(self.glo))