Build: Only checkout submodules for android

[softins]

Short description of changes

Only the Android build makes use of the submodule for oboe, so no need to fetch it when building other architectures.

CHANGELOG: Build: checkout of submodules only needed for Android

Context: Fixes an issue?

This just avoids unnecessary work in the CI when building targets other than Android.

Does this change need documentation? What needs to be documented and how?
I wouldn't have thought so.

Status of this Pull Request
Ready

What is missing until this pull request can be merged?
Nothing

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[ann0see]

Looks sensible. The build would not succeed if they aren't checked out?

[softins]

The build would not succeed if they aren't checked out?

That's correct, because each CI build starts with a clean instance.