fix: `manual_unwrap_or_default` suggests error when expression is a None variant

[t-webber]

Suggesting error when expression is none : None.unwrap_or_default() raises an error, as explained in the following issue:

fixes #12670

changelog: [manual_unwrap_or_default]: the lint is ignored when matching None, as the unwrap_or_default method can't infer the type of a None variant.

[rustbot]

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[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git rebase -i master
$ # delete any merge commits in the editor that appears
$ git push --force-with-lease

The following commits are merge commits:

• f97d38efd1e6a72a290e17f6aaa250e3a4cf1d01

[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git rebase -i master
$ # delete any merge commits in the editor that appears
$ git push --force-with-lease

The following commits are merge commits:

• 1d9e0cdde74dbe3508a700ee56e36556ab966248
• f97d38efd1e6a72a290e17f6aaa250e3a4cf1d01