`NotImplemented` is never tested with attribute assignment

[sobolevn]

Bug report

This issue adds tests for NoDefault and attribute assignment: #118895

But, we never had tests for the same thing of NotImplemented. I will add a test case for that.

Linked PRs

• gh-118899: Add tests for NotImplemented attribute access #118902
• [3.13] gh-118899: Add tests for NotImplemented attribute access (GH-118902) #118968
• [3.12] gh-118899: Add tests for NotImplemented attribute access (GH-118902) #118969