Switch GitHub actions to Node20

[stoecker]

​https://github.com/JOSM/josm/actions/runs/8821262311

says

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20:
JOSM/JOSMPluginAction/actions/checkstyle@v1. For more information see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Actually the link did not help to tell me what and where I need to change anything.

Anybody who can solve this?

[taylor.smock]

I've updated almost everything from node16 to node20. For the one you linked, I think I just have to update v1 to v2 in the tag.

For ​https://github.com/JOSM/josm/actions/runs/8828910217, I need to move us off of those actions, since they are no longer supported (thanks GitHub...).

[stoecker]

In 19059/josm:

drop node16 and Java8, see #23643

[stoecker]

​https://github.com/JOSM/josm/actions/runs/8839827951 also said "Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: JOSM/JOSMPluginAction/actions/pmd@v1." I hope r19059 catches this.

[taylor.smock]

My bad on missing pmd. It looks like r19059 ​fixed it.
The only thing left is the build stage, and specifically uploading the jars and installers to a release. I've been fiddling with that in a ​test-ci branch.

It does look like we'll need to do something with ProjectionRegressionTest on mac/Windows. And something for DateUtilsTest as well (it looks like Java 22 is returning CET like we used to get with the COMPAT/JRE locale provider).

[taylor.smock]

In 19061/josm:

Fix #23643: Move to supported actions for GitHub ant workflow to remove node16 deprecation warnings