Break up CI workflows in the build and test #287

What is the problem or limitation you are having?

The current CI workflows compile for each platform, and then test iOS. However, the test phase is part of the build target - so if there's a transient failure that causes the test suite to fail to start, it is necessary to perform a full rebuild of the iOS codebase.

Describe the solution you'd like

The build and test phases should be separate, with test dependent on build.

Describe alternatives you've considered

• Status quo.
• Work out why the iOS test suite fails to identify a start, and fix that.

Additional context

No response