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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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/servo/fake-ld.sh

@@ -9,7 +9,7 @@ set -o nounset
 set -o pipefail
 
 TARGET_DIR="${OUT_DIR}/../../.."
-arm-linux-androideabi-gcc "$@" \
+arm-linux-androideabi-gcc "${@}" \
                           "${LDFLAGS-}" -lc -shared \
                           -o "${TARGET_DIR}/libservo.so"
 touch "${TARGET_DIR}/servo"