Update GHA runners to macos-12

[DimitrisStaratzis]

This PR was originally opened by @jdblischak (#13). The CI in his PR fails because PRs from external contributors do not have access to the repo's secrets. In this case there is a repo secret in the form of an API token that gives access to TileDB-Cloud arrays.

[teo-tsirpanis]

I'm actually wondering if running CI on macOS is even worth it in the first place. This library is 100% Java code with no direct native dependencies or platform-specific code, and macOS runners are a scarce resource.

[teo-tsirpanis]

Use macos-latest like Ubuntu?

[DimitrisStaratzis]

macos-latest is a dynamic image, so i am trying to avoid updates that could lead to breaking changes. With this in mind we should consider using ubuntu-22.04 instead of ubuntu-latest

[DimitrisStaratzis]

I'm actually wondering if running CI on macOS is even worth it in the first place. This library is 100% Java code with no direct native dependencies or platform-specific code, and macOS runners are a scarce resource.

We very rarely run the Ci in this repo and the execution time when it runs is less than a minute. It is good in my opinion to test as many platforms as possible.

[ihnorton]

It is good in my opinion to test as many platforms as possible.

+1. If it becomes too frequent then we could make macOS nightly only, but it is still good to have a minimal check on all platforms.