Apply suggestions from code review

Co-authored-by: Alex Waygood <[email protected]>

Author: JelleZijlstra

src/typing_extensions.py

@@ -334,7 +334,7 @@ class Solid2: pass
 
             class Solid3(Solid1, Solid2): pass  # Type checker error
 
-        Type checkers can use solid bases to detect unreachable code
+        Type checkers can use knowledge of solid bases to detect unreachable code
         and determine when two types can overlap.
 
         See PEP 800."""