gh-107446: Fix test_inspect.test_class_with_method_from_other_module under --forever

[gaogaotiantian]

The test creates a temporary directory to store the modules every time it executes. However, with --forever, the test will run more than once. When the old directory got removed, the cached module would lost source. In order to fix this, we can simply remove the module from sys.modules and force the module to be reloaded every time.

• Issue: test_inspect fails with --forever argument #107446

[Eclips4]

Thanks for the fix!
Just FYI, I've found it via running refleak tests with 3:3 option. Probably, it's has the same mechanism of running tests as the --forever parameter.