Upgrade to pytest 8 for tests

I had some problems with pytest-selenium using pytest 8, so I pinned it to <8.0.0. There is a release of pytest-selenium that should work wtih an 8.* version, but it did not work out of the box when I tried. Also coverage had some problems with this option `-o testpaths="tests tests/notebooks/*py"`, the option name might have changed.
