doc: Fix the inline comment for proposalAccepted

[malturki]

Summary

This PR fixes what looks like a copy-paste error in the inline comment for the proposalAccepted event type in agreement/events.go.

Test Plan

No actual changes to the code are made, and thus no need for a specific test plan.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #4889 (e2e5b42) into master (92bb3ce) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4889      +/-   ##
==========================================
+ Coverage   53.57%   53.60%   +0.03%     
==========================================
  Files         430      430              
  Lines       54091    54091              
==========================================
+ Hits        28979    28997      +18     
+ Misses      22868    22855      -13     
+ Partials     2244     2239       -5     

Impacted Files	Coverage Δ
agreement/events.go	61.62% <ø> (ø)
ledger/catchpointtracker.go	57.70% <0.00%> (-0.80%)	⬇️
ledger/tracker.go	75.10% <0.00%> (ø)
network/wsNetwork.go	64.92% <0.00%> (+0.17%)	⬆️
ledger/acctonline.go	79.16% <0.00%> (+0.52%)	⬆️
ledger/testing/randomAccounts.go	56.88% <0.00%> (+0.61%)	⬆️
catchup/service.go	70.04% <0.00%> (+0.72%)	⬆️
network/wsPeer.go	68.79% <0.00%> (+2.36%)	⬆️
ledger/blockqueue.go	84.94% <0.00%> (+2.68%)	⬆️

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[cce]

Thanks!