Update requirements with new format for git

Update the requirements.txt with the new module @ git... format for
python-apt that works much better with pip 22+; this is so that pip
*doesn't* go to pypi to try to resolve the module if it doesn't 'match'
as the module is more formally defined (although it might just be a bug
in pip).

Also bump python-apt to 2.5.3 tag as that's the latest version.

requirements.txt

@@ -1,3 +1,4 @@
+python-apt @ git+https://git.launchpad.net/[email protected]
 ruamel.yaml
 theblues
 libcharmstore
@@ -9,9 +10,6 @@ SecretStorage  # LP: #1923727
 macaroonbakery
 pymacaroons
 tenacity
-distutils-extra-python  # needed by python-apt
-# python-apt available in pypi is too old, so using upstream's git repo with a tag.
-git+https://git.launchpad.net/[email protected]#egg=python-apt
 charmcraft<3.0  # stick to the 2.x series
 # to generate html reports
 Jinja2