Closing bugs as fixed (in master) what version for "fixed in" ?

[Jack via KMyMoney-devel]

I think there has been (and will be) more than one bug which has been  
closed as "RESOLVED FIXED" but it is fixed only in master, and not  
likely or not possible to backport to 5.1.x.  I'd love to be able to  
put a "Fixed in" version in those bugs, but not sure what to use.  I  
don't think 6.0 would be appropriate, as I would only use that number  
for a version totally and exclusively for Qt 6.  Is 5.2 reasonable, or  
is there a reason to just not use a version number in such cases.

Jack