Fix RaisesGroup calling check() on contained exceptions instead of Ex…

[kelliott1]

Fix RaisesGroup incorrectly calling check() on contained exceptions.

Files changed:
raises.py
raises_group.py (tests)

Problem:
RaisesGroup(..., check=...) invoked the check callback twice:
- once with the ExceptionGroup (correct)
- once with a contained exception (incorrect)

This could cause unexpected errors (e.g. AttributeError) and violated the documented behavior.

Fix:
Removed the extra invocation of check() on contained exceptions.
Ensured check() is only called with the ExceptionGroup.
Adjusted suggestion logic to avoid reusing the callback.

Tests:
Updated test_check() expectations.
Added regression test to ensure check() is called once and only with the group.

Result:
check() now behaves as documented and no longer receives contained exceptions.