Fix ./gradlew lint warnings

#### Steps to reproduce

1. Run `./gradlew lint` and address all warnings presented (you can see warnings reported in here: https://github.com/googlemaps/android-maps-ktx/actions/runs/109748915).

#### Code example

```
./gradlew lint
```

#### Stack trace
```
w: /Users/chrisarriola/workspace/android-maps-ktx/maps-v3-ktx/src/main/java/com/google/maps/android/ktx/MapFragment.kt: (25, 2): This class can only be used with the compiler argument '-Xopt-in=kotlin.RequiresOptIn'
```