Update supported Go versions

[SuperQ]

Now that 1.23 is out, update the supported version matrix to Go 1.21 through 1.23. This allows us to start using log/slog.

• Update generated tests.

[ArthurSens]

Hmmm, strange that we got failing tests with 1.23 🤔

We also want to generate the tests for new metrics for gocollector with 1.23. We have generation scripts[1][2] for that but the result[3] is showing that we've changed the generated files manually and CI didn't block it 😬.

I'm not sure how to proceed here, but it seems like we need to work on this[4] before updating the go version?

[SuperQ]

I've re-generate and manually fixed up the tests. I'd rather not block keeping things up-to-date on automation technical debt.

I need this for #1601.

When the review here is complete, I will update the required tests, as this is manually done in the GitHub UI.

[ArthurSens]

I've re-generate and manually fixed up the tests. I'd rather not block keeping things up-to-date on automation technical debt.

I need this for #1601.

When the review here is complete, I will update the required tests, as this is manually done in the GitHub UI.

Fair point. We can work on the automation later