check keys registered in add_invulnerable too

[girazoki]

Pass the check to add_invulnerable too, a check that only existed in set_invulnerables

[github-actions]

Coverage Report

(master)

@@                       Coverage Diff                        @@
##           master   girazoki-invulnerables-fixes      +/-   ##
================================================================
+ Coverage   75.93%                         76.31%   +0.38%     
  Files         107                            107              
- Lines       26739                          26694      -45     
================================================================
+ Hits        20303                          20370      +67     
- Misses       6436                           6324     -112     

Files Changed	Coverage
/node/src/chain_spec/dancebox.rs	95.24% (-0.02%)	🔽
/node/src/chain_spec/flashbox.rs	70.30% (-0.11%)	🔽
/pallets/configuration/src/lib.rs	85.66% (+0.41%)	🔼
/pallets/invulnerables/src/lib.rs	84.09% (+0.09%)	🔼
/runtime/dancebox/src/lib.rs	81.91% (+1.68%)	🔼
/runtime/flashbox/src/lib.rs	45.29% (+9.04%)	🔼
/runtime/flashbox/tests/common/mod.rs	99.71% (+1.77%)	🔼

Coverage generated Fri Feb 9 08:54:00 UTC 2024