Stabilize IOS CI

[clangenb]

We have two problems:

• Unstable Docker Performance (to run the encointer node)
• Unstable IOS Simulator Performance

Upgrading to later macOS images would probably resolve the IOS Simulator stability issues. However, nested hardware virtualization is not supported at all currently with new images (which implies that we can't use docker within a GitHub actions runner). So for now, we can either:

• Accept the unstable state, and hope that we have nested virtualization support before macos13 runner images are end of life.
• Build an macOS encointer-node binary that we can use in the CI. But this means a lot of hussle, as we need to download an artifact, and also the client binary, and make sure that the bootstrapping script is available too in the CI...

Currently, I opt for just waiting to see if the situation improves. We can't be the only ones that need docker on a macOs CI.

[clangenb]

We are now hitting the first issue:

• Mobile scanner can't be upgraded to 6.0.0 because it requires xcode v15.3.0, which needs macos > 14.

Nothing urgent yet, but who knows when something else requires xcode v15.3.0. Apple is quite strict with requiring their devs to follow the upgrade cycles.