C#: Ignore late bound methods in MustBeVariantAnalyzer

[raulsntos]

If symbol is late bound (as is the case when using dynamic) we can't obtain the symbol to analyze the usage of [MustBeVariant].

• Fixes https://github.com/godotengine/godot/issues/91345.

[akien-mga]

Is this safe (and worth it) to cherry-pick for 4.2?

[raulsntos]

It's safe but will likely not cherry-pick cleanly because of surrounding changes. I don't think it's worth cherry-picking though since dynamic is pretty much discouraged these days.

[paulloz]

Maybe adding a test, to prevent future regressions 👀

[akien-mga]

Thanks!