[typing] Fix minor typing of pip._internal sub packages utils, exceptions, locations, self_outdated_check

[pelson]

Follows on from issues identified through #13599.

As before, intentionally targeting zero functional change.

[sepehr-rs]

Hi @pelson, thanks again for your contribution to pip!
This PR appears to be mostly internal again, so I’ve added the 'skip news' label.
Since these typing improvements seem related, it might be worth considering grouping similar changes into a single PR in the future, which can sometimes make reviews a bit easier for maintainers.
In any case, thanks for working on improving the typing coverage here!

[ichard26]

Looks good other than the one rewrite you suggested and I prefer that we went with.

[uranusjr]

I’m just curious why this annotation is even needed. Shouldn’t the return type be inferred…?

[pelson]

Yes, you are right. I checked with both our existing mypy calls and with the full mypy in #13599, and in both cases reveal_type correctly gives us the install command class as the type.

I've added a commit.