Properly recognized non-class types as internal when using HaveAccessModifier assertion

[jonathonchase]

Removes IsClass check preventing enums and interfaces from being recognized as internal types when not nested.

Fixes #1741

IMPORTANT

• The code complies with the Coding Guidelines for C#.
• The changes are covered by a new or existing set of unit tests which follow the Arrange-Act-Assert syntax such as is used in this example.
• If the contribution adds a feature or fixes a bug, please update the release notes, which are published on the website.
• If the contribution changes the public API the changes needs to be included by running AcceptApiChanges.ps1/AcceptApiChanges.sh.
• If the contribution affects the documentation, please include your changes in this pull request so the documentation will appear on the website.

[jonathonchase]

Closes #1741

[jonathonchase]

This is my first time contributing, and I'm not sure if the check list is something I should be filling out, or if that's in place for a maintainer to fill.

[dennisdoomen]

Could you please give the PR itself also a functional description, for instance, by reusing part of the release notes? Because the title will appear in the auto-generated Github release note.

[jnyrup]

We should also test enums and structs.
You could modify
When_asserting_an_internal_type_is_internal_it_succeeds and When_asserting_an_internal_type_is_protected_internal_it_throws
from a [Fact] to a [Theory] covering class, interface, enum, struct.

[dennisdoomen]

@jonathonchase are you planning to follow-up on @jnyrup's comments?

[dennisdoomen]

Replaced by #1793