gh-91539: improve performance of get_proxies_environment (GH-91566)

* improve performance of get_proxies_environment when there are many environment variables

* 📜🤖 Added by blurb_it.

* fix case of short env name

* fix formatting

* fix whitespace

* whitespace

* Update Lib/urllib/request.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Update Lib/urllib/request.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Update Lib/urllib/request.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Update Lib/urllib/request.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

* whitespace

* Update Misc/NEWS.d/next/Library/2022-04-15-11-29-38.gh-issue-91539.7WgVuA.rst

Co-authored-by: Carl Meyer <carl@oddbird.net>

* Update Lib/urllib/request.py

Co-authored-by: Carl Meyer <carl@oddbird.net>

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Carl Meyer <carl@oddbird.net>
(cherry picked from commit aeb28f51304ebe2ad9fd6a61b6e4e5a03d288aa1)

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>