Python3.9 dependency range correction

[reactive-firewall]

This change is to fix GHI #3037

Just corrects the upper limit of pre-3.10 Python filelock to the version 3.19.1

Should be transparent to users of Python 3.10+

Refs:

• Incorrect dependency range specified for python 3.9 (e.g., macOS xcode python3.9) #3037

• virtualenv/pyproject.toml

  Lines 48 to 49 in 9719376

  	"filelock>=3.16.1,<4; python_version<'3.10'",
  	"filelock>=3.20.1,<4; python_version>='3.10'",

• development documentation)
• https://pypi.org/project/filelock/3.19.1/ (see trove classifier python :: 3.9 present)
• https://pypi.org/project/filelock/3.20.0/ (see trove classifier python :: 3.9 removed)

[reactive-firewall]

@gaborbernat I saw your merge on main and rebased this PR so both this fix and the discussed version bump for python 3.10+ would be based off the same point along main, yet can be tested, merged separately.

🙇 hopefully this is helpful, and not an additional maintenance burden.