sre_constants is deprecated

[oliver-sanders]

The sre_constants module is now deprecated at Python 3.11 for removal in Python 3.13.

https://docs.python.org/3/whatsnew/3.11.html#modules

[MetRonnie]

isodatetime/metomi/isodatetime/parsers.py

Lines 344 to 347 in 658b31e

	try:
	compiled_regex = re.compile(regex)
	except sre_constants.error:
	raise StrptimeConversionError(source, regex)

Probably can just replace with Exception. The line in question is showing as not covered by tests so could do with adding a few while we're at it