typing: Make less use of ParamSpec

This is a partial revert of 1078647.
mypy (and possibly others) are not able to correctly resolve a ParamSpec
for an overridden method. This causes a lot of false positives when
using assertRaises (as a function) on methods with overrides, which
cannot be resolved except through `type: ignore` statements. In
addition, it's often desirable to test functions with incorrect types to
assert runtime validation. Given these two issues, it's easier to just
drop the use of ParamSpec.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

testtools/testcase.py

@@ -577,18 +577,18 @@ def assertIsInstance(  # type: ignore[override]
     def assertRaises(
         self,
         expected_exception: type[_E],
-        callable: Callable[_P, _R],
-        *args: _P.args,
-        **kwargs: _P.kwargs,
+        callable: Callable[..., Any],
+        *args: Any,
+        **kwargs: Any,
     ) -> _E: ...
 
     @overload
     def assertRaises(
         self,
         expected_exception: tuple[type[BaseException], ...],
-        callable: Callable[_P, _R],
-        *args: _P.args,
-        **kwargs: _P.kwargs,
+        callable: Callable[..., Any],
+        *args: Any,
+        **kwargs: Any,
     ) -> BaseException: ...
 
     @overload