I asked for it in !370 (comment 955663). Nothing wrong with const but for parameters passed by value, imho it's an implementation detail and what the function body does with it that shouldn't be prescribed at an API level.
Plus, if we use const here, for consistency we'd also have to add it to other parameters (perhaps all parameters?) such as the QString action above, which in addition to verbosity makes it harder to spot the difference between value const QString and const-ref const QString &.