ci: use Cirrus Runners for iOS Integration Tests

### Description

GitHub-hosted Runners keep pulling the rug under our feet, removing Xcode versions older than the latest 3 versions.
This semi-regularly, but continuously, breaks our CI.
We are in dire need of a stable Environment.

Cirrus Labs Runners to the rescue.
See also: https://github.com/getsentry/sentry-react-native/pull/5485

### Tasks
- switch .NET MAUI 9.0 Integration Tests for iOS to Cirrus Labs Runners
- switch .NET MAUI 10.0 Integration Tests for iOS to Cirrus Labs Runners

See
- https://github.com/getsentry/sentry-dotnet/pull/4750#discussion_r2771172008
- https://github.com/getsentry/sentry-dotnet/pull/4750#discussion_r2771196644
- https://github.com/getsentry/sentry-dotnet/pull/4750#discussion_r2771203245
- https://github.com/getsentry/sentry-dotnet/pull/4750#discussion_r2771228831
- https://github.com/getsentry/sentry-dotnet/pull/4750#discussion_r2771229219