Fix: Lambda expression

[hlaueriksson]

Invoking a test fixture member with a lambda expression resulted in a crash:

Message:
  System.ArgumentOutOfRangeException : StartIndex cannot be less than zero. (Parameter 'startIndex')
Stack Trace:
  String.Remove(Int32 startIndex)
  InternalNamingExtensions.GetFunctionName(MethodInfo testFunction, MethodBase testMethod)
  LoFuTest.AssertAsync(Object testFixture, MethodBase testMethod)
  InternalLoFuTestExtensions.AssertAsync(Object fixture, MethodBase method)
  <.ctor>b__0_0(TestExecutionContext context)
  AfterTestCommand.Execute(TestExecutionContext context)
  SimpleWorkItem.PerformWork()

This would for example happen when using FluentAssertions and testing exceptions:

Func<Task> act = () => asyncObject.ThrowAsync<ArgumentException>();
await act.Should().ThrowAsync<InvalidOperationException>();

See https://fluentassertions.com/exceptions/