Auto merge of #12736 - aneeshusa:prohibit-backticks-in-shell-scripts, r=Wafflespeanut

Add more shell script lints

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The "$(some_command arg1 arg2)" form is preferred to the
`some_command arg1 arg2` form because it nests unambiguously.
Add a lint for this to tidy.

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- [ ] These changes fix #__ (github issue number if applicable).

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