pytest 8.0.0 changes

[DougBurke]

We now have pytest 8.0.0 on some of our CI runs and I point out, from the 8.0.0 changelog (currently https://docs.pytest.org/en/stable/changelog.html ) the following nugget

• #9288: warns() now re-emits unmatched warnings when the context closes – previously it would consume all warnings, hiding those that were not matched by the function.

  While this is a new feature, we announce it as a breaking change because many test suites are configured to error-out on warnings, and will therefore fail on the newly-re-emitted warnings.

since I just got a test failure because of this that looks exactly like this issue:

-------------------------- Captured stdout teardown ---------------------------
*** Warnings created: 1
1/1 {message : FutureWarning('calc() requires pars,rhs,lo,hi arguments, sent 3 arguments'), category : 'FutureWarning', filename : '/home/runner/work/sherpa/sherpa/sherpa/astro/xspec/__init__.py', lineno : 1591, line : None}

----------- coverage: platform linux, python 3.9.0-final-0 -----------

[DougBurke]

I hopefully have a fix for this in b2acc78