Tests: Cast unused smart-pointer return values to void

Author: https://github.com/AtkinsSJ
Commit: 9e3a786a64
Pull-request: https://github.com/SerenityOS/serenity/pull/11151

Tests/LibJS/test-js.cpp

@@ -20,7 +20,7 @@ TESTJS_GLOBAL_FUNCTION(can_parse_source, canParseSource)
 {
     auto source = TRY(vm.argument(0).to_string(global_object));
     auto parser = JS::Parser(JS::Lexer(source));
-    parser.parse_program();
+    (void)parser.parse_program();
     return JS::Value(!parser.has_errors());
 }