update CI versions to Julia 1.11 (current) and 1.10 LTS

[colinleach]

Some extracts from a recent Julia Language notification:

The Julia developers are pleased to announce the release of Julia v1.11.0, the eleventh minor release in the 1.x series.

As a minor release, v1.11.0 contains no breaking changes, only new features, performance improvements, and marginal, non-disruptive changes in behavior.

We are also pleased to announce that Julia 1.10 is now the current long-term support (LTS) release, replacing 1.6.

With this, Julia 1.6 is now officially unmaintained.

I propose to drop 1.6 testing, switching to 1.11, 1.10 and nightly. I ran the CI workflow on my branch: it completed successfully in under 3 minutes.

With 1.6, we had both MacOS compatibility issues and very slow (15-20 min) CI on Windows, so I will be very happy to remove it.

@exercism/cross-track-maintainers, there was a suggestion in #793 to do cross-OS testing only on the LTS branch and Ubuntu-only on the newer versions. Is that something to consider here? It's less urgent once we have much faster CI overall (also, I'm unsure how best to code it in exercise-test.yml, and I'm trying to minimize destructive trial and error).

[BethanyG]

@exercism/cross-track-maintainers, there was a suggestion in #793 to do cross-OS testing only on the LTS branch and Ubuntu-only on the newer versions. Is that something to consider here? It's less urgent once we have much faster CI overall (also, I'm unsure how best to code it in exercise-test.yml, and I'm trying to minimize destructive trial and error).

If the CI is now speedy with the dropping of 1.6, I'd say leave it as-is. If you then run into speed issues with the new matrix, you can start excluding problematic OSs at that point.

[depial]

@colinleach this doesn't show up for you? I wonder what the issue could be?

[colinleach]

OK, I see that now. Being specific about the current release ("1.11" rather than "1") isn't my idea, it is apparently an Exercism standard. The thinking is that it minimizes unexpected compatibility problems.

In short, I changed it because I was told to.

[colinleach]

Great! It will be good to leave 1.6 behind us, with all its problems.