fix(eslint-plugin): [strict-bool-expr] allow nullish coalescing

[bradzacher]

This rule shouldn't actually touch them, but it never checked the operator, so it does right now..

[typescript-eslint]

Thanks for the PR, @bradzacher!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[ShayDavidson]

Thanks for this! 🙏 This has been the only blocker for me for using null coalescing.