Upgrade flake8-import-order and flake8-requirements

[loqs]

What do these changes do?

These packages were using the deprecated pkg_resources module which has been removed from setuptools in version 82.0.0, causing flake8 to fail with 'ModuleNotFoundError: No module named pkg_resources'.

• flake8-import-order: 0.18.2 -> 0.19.2
• flake8-requirements: 2.2.1 -> 2.3.0

Are there changes in behavior for the user?

No

Related issue number

Fixes the continuous integration failure in #568.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• tox testenvs have been executed in the following environments:
  • Linux (Ubuntu 18.04, Ubuntu 20.04, Arch): python -m flake8 aiosmtpd
  • Windows (7, 10): {py36,py37,py38,py39}-{nocov,cov,diffcov}
  • WSL 1.0 (Ubuntu 18.04): {py36,py37,py38,py39}-{nocov,cov,diffcov}, pypy3-{nocov,cov}, qa, docs
  • FreeBSD (12.2, 12.1, 11.4): {py36,pypy3}-{nocov,cov,diffcov}, qa
  • Cygwin: py36-{nocov,cov,diffcov}, qa, docs
• Documentation reflects the changes
• Add a news fragment into the NEWS.rst file

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.78%. Comparing base (fd1fd7e) to head (c94ba70).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #572      +/-   ##
==========================================
- Coverage   97.86%   97.78%   -0.08%     
==========================================
  Files          23       23              
  Lines        5701     5701              
  Branches      766      766              
==========================================
- Hits         5579     5575       -4     
- Misses         77       80       +3     
- Partials       45       46       +1     

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[webknjaz]

Codecov says there's some coverage drop, but it doesn't seem related. So I'll merge this bump regardless.