Limit block production to one block per slot in basic collator

[Agusrodri]

Fixes the following panic present in the logs:

2024-03-13 16:56:06.023  INFO tokio-runtime-worker sc_basic_authorship::basic_authorship: [Container-2002] :raised_hands: Starting consensus session on top of parent 0x35551d29498f418c033e7faa19b69df6b8df0f7cffbdce9ca4076a95efd6ad29    
2024-03-13 16:56:06.024 ERROR tokio-runtime-worker runtime: [Container-2002] panicked at /home/builder/cargo/git/checkouts/moonkit-c6defa46a244ac75/9d006f9/pallets/async-backing/src/consensus_hook.rs:73:21:
Block invalid; Supplied slot number is not high enough

As related to paritytech/polkadot-sdk#3308, it seems that with the current configuration of the basic collator, every para-block is attempted to be imported twice in the same slot, which is not the expected case with this "basic" kind of collator.

[girazoki]

ty agustin!

[github-actions]

Coverage Report

(master)

@@                         Coverage Diff                          @@
##           master   agustin-fix-basic-collator-panic      +/-   ##
====================================================================
- Coverage   67.72%                             67.56%   -0.16%     
  Files          63                                 63              
+ Lines        9143                               9161      +18     
====================================================================
- Hits         6192                               6189       -3     
+ Misses       2951                               2972      +21     

Files Changed	Coverage
/client/consensus/src/collators.rs	81.12% (-0.79%)	🔽
/pallets/pooled-staking/src/candidate.rs	95.45% (-1.01%)	🔽

Coverage generated Wed Mar 13 20:42:22 UTC 2024