Method type argument inference and local variable

This is probably caused by #979, but the interaction with a local variable seems strange.

Run the Nullness Checker on:

import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

abstract class Demo {
  class Box<R> {}

  abstract <S> S unbox(Box<S> b);

  abstract <T> @NonNull T checkNotNull(@Nullable T sample);
  
  void test(Object s) {}
  
  void bar(Box<?> s) {
    test(checkNotNull(unbox(s)));

    Object o = checkNotNull(unbox(s));
    test(o);
  }
}

The first invocation test(checkNotNull(unbox(s))); type checks.

Putting the argument to test into a local variable causes a argument.type.incompatible error.

The method type argument inference in that case cannot use the assignment context, but should still consider the explicit @NotNull annotation on the checkNotNull return type.