Silence packaging 20.5 deprecation warnings

[antonio-rojas]

packaging 20.5 throws lots of deprecation warnings

/usr/lib/python3.9/site-packages/packaging/version.py:127: DeprecationWarning: Creating a LegacyVersion has been deprecated and will be removed in the next major release

when called from setuptools when building the module index (which happens indirectly eg. when calling sage_getdoc). We silence these warnings, since this is really out of sage's control (even if all of sage's python packages were fixed, this could still be triggered by packages installed with sage-pip, or by any other python package in the case of distro packages)

CC: @dimpase @mkoeppe @kiwifb

Component: packages: standard

Author: Antonio Rojas

Branch/Commit: dca89b2

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30975

[antonio-rojas]

Branch: u/arojas/silence_packaging_20_5_deprecation_warnings

[antonio-rojas]

Commit: 7dbcd04

[mkoeppe]

Changed branch from u/arojas/silence_packaging_20_5_deprecation_warnings to u/mkoeppe/silence_packaging_20_5_deprecation_warnings

[mkoeppe]

Author: Antonio Rojas

[mkoeppe]

Reviewer: Matthias Koeppe

[mkoeppe]

Changed commit from 7dbcd04 to dca89b2

[mkoeppe]

New commits:

dca89b2

build/pkgs/packaging/install-requires.txt: Add comment on version 20.5

[mkoeppe]

comment:5

(see #30719)

[vbraun]

Changed branch from u/mkoeppe/silence_packaging_20_5_deprecation_warnings to dca89b2