ci: add CI for apple mobile platforms

[res0nance]

Adds CI for Apple mobile platforms.

Unfortunately I'm not sure how to effectively run the tests within the emulator. Plus it will likely be incredibly flaky. I think we should compile test this until we can figure out how to better run the full suite of tests.

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in oqs-provider, OQS-OpenSSL, OQS-BoringSSL, and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[baentsch]

LGTM. Brings build-testing to the same level as for android (#1531). Thanks for the contribution!