Add Python 3.9 holdbacks for 12 more packages

A broader requires_python sweep against PyPI showed that the latest
versions of black, cfgv, click, filelock, flake8-bugbear, identify,
isort, platformdirs, pre-commit, pycparser, requests, and urllib3 all
declare requires_python >= 3.10. Pip on Python 3.9 refused to resolve
the requirements file partway through; the build halted at black.

For each affected package, pin the latest 3.9-compatible release for
the < 3.10 branch and keep the current latest for >= 3.10. Verified
that 3.10, 3.11, 3.12, 3.13, 3.14 are unaffected — no packages
exclude those versions at their latest pins.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

requirements_recommended.txt

@@ -56,12 +56,3 @@ urllib3==2.7.0; python_version >= "3.10"
 urllib3==2.6.3; python_version < "3.10"
 virtualenv==21.3.2
 xattr==1.3.0
-pyobjc==11.1
-PyYAML==6.0.2
-requests==2.32.4
-six==1.17.0
-tokenize-rt==6.2.0
-tomli==2.4.1
-urllib3==2.7.0
-virtualenv==21.3.2
-xattr==1.3.0