getPayload: log info only if request was cancelled because another relay delivered the payload already

[metachris]

📝 Summary

• If two relays delivered the same bid, mev-boost would ask the payload from both relays.
• As soon as one relay delivers the payload, the request to the other relay is cancelled.
• This change will only log the information that the request was cancelled instead of logging an error

---

✅ I have run these commands

• make lint
• make test-race
• go mod tidy

[codecov-commenter]

Codecov Report

Merging #356 (0ae4a0b) into main (af2741f) will increase coverage by 0.08%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #356      +/-   ##
==========================================
+ Coverage   81.44%   81.52%   +0.08%     
==========================================
  Files           5        5              
  Lines         679      682       +3     
==========================================
+ Hits          553      556       +3     
- Misses         96       97       +1     
+ Partials       30       29       -1     

Flag	Coverage Δ
unittests	81.52% <0.00%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/service.go	79.41% <0.00%> (+0.15%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.