Fix: avoid indent and no-mixed-spaces-and-tabs conflicts (fixes #7248)

[not-an-aardvark]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

See #7248

Please check each item to ensure your pull request is ready:

• I've read the pull request guide
• I've included tests for my change
• (n/a) I've updated documentation for my change (if appropriate)

What changes did you make? (Give an overview)

This updates indent to not report lines that have mixed spaces and tabs, to avoid conflicts with the no-mixed-spaces-and-tabs rule.

I think this is better than reverting 8b3fc32, because if that commit is reverted, then indent's autofix will be broken again on lines containing mixed spaces and tabs (see #4274).

Is there anything you'd like reviewers to focus on?

Nothing in particular.

[eslintbot]

LGTM

[platinumazure]

LGTM, thanks very much for writing this up so quickly.

[nzakas]

LGTM