Drop support for PySide2

[nicoddemus]

PySide2 is no longer maintained, with the last release being made in 2022.

Follow-up to #572 (comment).

@The-Compiler I like the removed cruft and CI jobs, but I understand if you would like to keep the support around.

[The-Compiler]

Seems fine other than the tests I commented on. Personally I'd still keep it for another ~2 years (Python 3.10 EOL -> not possible to run anymore on any supported Python) given that it's not really in the way. But I'm also fine with getting rid of it, given that Qt 6.0 is 4 years old already, and 6.2 (first release with e.g. QtWebEngine available) has been around for more than 3 years. Time flies!

[The-Compiler]

I'm a bit confused by the current situation here (also for the test below) - is this really only relevant for PySide2, or did we just never add PySide6 to the test?

From what this looks like:

pytest-qt/src/pytestqt/wait_signal.py

Lines 104 to 123 in 89178ed

	def determine_signal_name(self, potential_signal_tuple):
	"""
	Attempts to determine the signal's name. If the user provided the signal name as 2nd value of the tuple, this
	name has preference. Bad values cause a ``ValueError``.
	Otherwise it attempts to get the signal from the ``signal`` attribute of ``signal`` (which only exists for
	PyQt signals).
	:returns: str name of the signal, an empty string if no signal name can be determined, or raises an error
	in case the user provided an invalid signal name manually
	"""
	signal_name = self._extract_signal_from_signal_tuple(potential_signal_tuple)
	if not signal_name:
	try:
	signal_name = self._extract_pyqt_signal_name(potential_signal_tuple)
	except AttributeError:
	# not a PyQt signal
	# -> no signal name could be determined
	signal_name = ""
	return signal_name

and from [PYSIDE-1911] Provide a way to get the name of a Signal(Instance) - Qt Bug Tracker only being partially fixed (I think we never implemented the "extract from repr" part?), I believe those tests should still be run on PySide6 actually?

[nicoddemus]

Ahh great catch! You are right, they should be running for PySide 6 too.

Brought the tests back and updated the condition.