Use Ubuntu 22.04 for CI

[DavidMStraub]

In #1858, I realized the CI currently runs on Ubuntu 20.04, which uses Python 3.8, that we are not supporting anymore. This PR switches conservatively to 22.04 LTS, which uses Python 3.10. One package had to be removed as well to make it run, but I believe this is anyway an old Python 2 leftover.

[Nick-Hall]

Thew new package name for python-libxml2 is python3-libxml2.

[dsblank]

LGTM!

[Nick-Hall]

56 unit tests are being skipped.

[DavidMStraub]

56 unit tests are being skipped.

But they are currently skipped everywhere, also on master.

Thew new package name for python-libxml2 is python3-libxml2.

Thanks, added back.

[Nick-Hall]

The tests that are skipped are from gramps.gen.merge.test.merge_ref_test and the message is:

skipped 'These tests need the 3rd-party plugins "CliMerge" and "ExportRaw".'

The gramps60 branch is not yet available for the addons, so this is understandable.

These are also the tests that require the lxml functionality.

[DavidMStraub]

I'm confused, nothing added in this PR changes the number of tests skipped compared to master, right?

[stevenyoungs]

A change in OS configuration?
The tests appear conditional on

gramps/gramps/gen/merge/test/merge_ref_test.py

Lines 44 to 45 in ca6205d

	HAS_CLIMERGE = os.path.isdir(os.path.join(USER_PLUGINS, "CliMerge"))
	HAS_EXPORTRAW = os.path.isdir(os.path.join(USER_PLUGINS, "ExportRaw"))

[Nick-Hall]

We are trying to load the v5.2 version of CliMerge and ExportRaw which is going to fail. The tests are then skipped.

Everything is working in the gramps52 branch. I checked the unit tests as part of the v5.2.4 release process.

[Nick-Hall]

Rebased.