fix macro when `ignore_index` is set

[edumotya]

What does this PR do?

Fixes #1691

Additionally, tests have been updated to exclude the ignored class from the macro accuracy averaging.

Before submitting

• [ ] Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• [ ] Did you read the contributor guideline, Pull Request section?
• [ ] Did you make sure to update the docs?
• [ ] Did you write any new necessary tests?

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:books: Documentation preview :books:: https://torchmetrics--2163.org.readthedocs.build/en/2163/

[Borda]

@edumotya how is it going, mind checking comment from Nicki

[Borda]

@edumotya seems like most of the tests are off; could you pls check it... turning it back to draft until most other checks are green... pls make it as ready to review when you resolve them... :flamingo:

[edumotya]

sure @Borda, I am sorry for the late response. It might take me some time, it is not straightforward to fix the affected tests, I'll do my best