[llvm] [llvm-lit][test] Precommit tests for curly braces in lit internal shell (PR #102976)

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connieyzhu wrote:

CC: @ilovepi @petrhosek @jh7370 

Hi there, I'm writing some tests for curly braces in lit's internal shell before I implement the functionality in https://github.com/llvm/llvm-project/pull/102830. I wasn't sure if I should write more in-depth tests in this patch, since the same syntax error will be given for every test at the moment, or if I should just include more tests in my later patch once I have implemented the proper functionality. 

https://github.com/llvm/llvm-project/pull/102976