LibJS: Propagate errors from VM creation

Author: https://github.com/trflynn89
Commit: 13dfadba79
Pull-request: https://github.com/SerenityOS/serenity/pull/17892
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibTest/JavaScriptTestRunnerMain.cpp

@@ -189,7 +189,7 @@ int main(int argc, char** argv)
         g_main_hook();
 
     if (!g_vm) {
-        g_vm = JS::VM::create();
+        g_vm = MUST(JS::VM::create());
         g_vm->enable_default_host_import_module_dynamically_hook();
     }