CI for mono support

[vaind]

Currently, the Mono scripting backend support is not tested in CI, even though in #751 we've enabled the native crash support.

What would need to be done to add this to CI:

• add the mono-specific build methods (or an argument) to https://github.com/getsentry/sentry-unity/blob/0.17.0/samples/unity-of-bugs/Assets/Editor/Builder.cs
• update symbol-upload test (expected symbol files)
• update the methods in the integration-test PowerShell scripts
• update ci.yml, of course

[vaind]

Unknown impact at the moment. May be re-prioritized