[clang] [clang][NFC] Reduce one of JSON dump tests (PR #195026)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

A simpler way to put it, is that if JSON dumper has equal footing to the Text dumper, then it would only be reasonable that the each test case tests both equally.

That makes life twice as hard when updating these tests, but at least that would be consistent.

https://github.com/llvm/llvm-project/pull/195026