Missing dev_flashbox flags

[fgamundi]

Fixes the unexpected behavior when running Moonwall test suite dev_flashbox, addressed by --reserved-only

[tmpolaczyk]

For the record, the issue was that moonwall spawns multiple nodes at once, and without the --reserved-only flag those nodes connected to each other. --dev already implies this flag, that's why the other tests work. Thank you for the detective work @fgamundi! I already tried this locally and it works. (I got a timeout error once but that's a known issue)

[github-actions]

Coverage Report

(master)

@@                  Coverage Diff                  @@
##           master   fg-flashbox-flags      +/-   ##
=====================================================
- Coverage   75.95%              75.94%   -0.01%     
  Files          97                  97              
  Lines       24332               24332              
=====================================================
- Hits        18481               18477       -4     
+ Misses       5851                5855       +4     

Files Changed	Coverage
/pallets/inflation-rewards/src/lib.rs	90.91% (-2.27%)	🔽
/pallets/registrar/src/lib.rs	91.93% (-0.25%)	🔽

Coverage generated Thu Dec 21 14:43:53 UTC 2023