Move back to mainline vcrpy with urllib3 2.x when possible

[dgw]

Follow-up to #2455. We only want this pinned temporarily, as described in 6e64c96; when possible, the pin should be removed.

Relies on resolution of upstream issue, kevin1024/vcrpy#688

[dgw]

#2519 made unpinning urllib3 possible, and the upstream issue in vcrpy has been "closed". But we're still doing Kludgy Things related to both packages:

sopel/dev-requirements.txt

Lines 20 to 22 in 973a489

	# use fork of vcrpy 5.x until kevin1024/vcrpy#777 is (hopefully) accepted
	# (or until py3.9 EOL... in 10/2025, I HOPE NOT)
	vcrpy @ git+https://github.com/sopel-irc/vcrpy@uncap-urllib3

I will retitle this issue to reflect the current state, which is that vcrpy might or might not ever officially support using urllib3 2.x on Python <3.10 given problems with vcrpy's test suite on those combinations. There's no guarantee that I'll ever manage to get my patch into a state acceptable to upstream (but the test failures happen only in the suite's "offline" mode that mocks out actual communication with a server, seeming to work just fine when talking to real servers).