Bug RUN_ONLY_MEMBERS is converting sets into list

The dummy experiment from the autosubmit tutorial doesn't work when using the version 3.13.0b, giving the next output error:

Critical Issues on [Expdef] config file:
[Default] Main platform is not defined! check if [HPCARCH = LOCAL] has any typo
 [eCode=7014]

The project is the a3f7. FYI: @dbeltran