Add type parameters for some generic types

[injust]

Changes

Add type parameters for some generic types (Callable, Iterable, and TaskStatus)

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) added which would fail without your patch
• You've updated the documentation (in docs/, in case of behavior changes or new
  features)
• You've added a new changelog entry (in docs/versionhistory.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
these instructions.

Updating the changelog

If there are no entries after the last release, use **UNRELEASED** as the version.
If, say, your patch fixes issue #999, the entry should look like this:

* Fix big bad boo-boo in the async scheduler (#999 <https://github.com/agronholm/apscheduler/issues/999>_; PR by @yourgithubaccount)

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.

[coveralls]

coverage: 92.217%. remained the same
when pulling 1eabad7 on injust:types
into 25cac59 on agronholm:master.

[injust]

This is pretty trivial, but it fixes some unknown types when using the library. Does it need a changelog entry?

[agronholm]

No, I don't think it warrants a changelog entry.

[agronholm]

Thanks!

[injust]

Ugh I missed one Callable because it was in a TypeAlias

#951