Current logic in `test_installed_modules` does not properly handle
distributions with underscores. On my machine I get the following error
while running tests:
```
tests/integrations/modules/test_modules.py:60: in test_installed_modules
    assert installed_modules == pkg_resources_modules
E   AssertionError: assert {'aiven-clien...'22.2.0', ...} == {'aiven-clien...'22.2.0', ...}
E     Omitting 93 identical items, use -vv to show
E     Left contains 1 more item:
E     {'tomli_w': '1.0.0'}
E     Right contains 1 more item:
E     {'tomli-w': '1.0.0'}
E     Use -v to get more diff
```

This change fixes distribution name normalization by applying the code
from PEP-0503 (https://peps.python.org/pep-0503/#normalized-names).

This reverts commit 0d301bb.