[Fix #7936] Mark as Lint/BooleanSymbol unsafe

[laurmurclar]

Fixes #7936

This PR marks Lint/BooleanSymbol as unsafe.

As mentioned in the issue, the auto-corrected code is not equivalent to the problem code and therefore can't be run safely without changing the meaning of the code.

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
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[laurmurclar]

I'm not sure why CI failed for windows 2.6, but it doesn't look related to this change 🤔

[koic]

I think this change makes sense because true (false) and :true (:false) are not equivalent.

[bbatsov]

I agree with the proposed change as well. Thanks!