[test] Fix SWIFT_STDLIB_SINGLE_THREADED_RUNTIME to be TRUE instead of YES

YES/NO style is not compatible with lit.site.cfg.in tempalte

Author: kateinoigakukun

cmake/caches/Runtime-WASI-wasm32.cmake

@@ -27,4 +27,4 @@ set(SWIFT_STDLIB_ENABLE_THINCMO YES CACHE BOOL "")
 # build with the host compiler
 set(SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER YES CACHE BOOL "")
 
-set(SWIFT_STDLIB_SINGLE_THREADED_RUNTIME YES CACHE BOOL "")
+set(SWIFT_STDLIB_SINGLE_THREADED_RUNTIME TRUE CACHE BOOL "")