[clang][ThreadSafety] Fix code block syntax in ThreadSafetyAnalysis.rst (#96494)
Without a newline, documentation was failing to build with this error:
Warning, treated as error:
/home/runner/work/llvm-project/llvm-project/clang-build/tools/clang/docs/ThreadSafetyAnalysis.rst:466:Error
in "code-block" directive:
maximum 1 argument(s) allowed, 10 supplied.
Issue #92408