qa: Don't return a const ref from Settings::localValue()

qa: Don't return a const ref from Settings::localValue()

Stumbled on this by accident because one particular CI configuration
warned about Settings::localValue() returning a stack reference
(may happen if the default value (which is a const ref itself) is
returned).

Not sure why I don't see this warning in my own setup, but it's
legitimate; thus fix the issue.