fix(x/gov): remove leading comma in proposal_messages event attribute (backport #26353)

[mergify]

Description

Closes: #26045

The proposal_messages event attribute was being built by prepending a comma to each message type URL inside the loop in x/gov/keeper/proposal.go:

msgsStr += fmt.Sprintf(",%s", sdk.MsgTypeURL(msg))

For a proposal with two messages, this emitted ",/cosmos.bank.v1beta1.MsgSend,/cosmos.staking.v1beta1.MsgDelegate" instead of "/cosmos.bank.v1beta1.MsgSend,/cosmos.staking.v1beta1.MsgDelegate". The leading comma broke downstream consumers that parse the attribute by splitting on commas (the first element comes back empty).

Changes

• Replace the manual msgsStr accumulator with a []string collected via append, then emit the joined value with strings.Join(msgTypeURLs, ",").
• Add TestSubmitProposal_EmitsMessagesWithoutLeadingComma regression test that submits a proposal with two messages and asserts the emitted attribute has no leading comma and equals the expected joined value.

I also checked CancelProposal for the same pattern (per the suggestion in the issue thread) — it does not emit a proposal_messages event, so no changes needed there.

A CHANGELOG entry will be added in a follow-up commit once this PR has a number.

---

This is an automatic backport of pull request #26353 done by Mergify.

[greptile-apps]

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• e69da8d — fix(x/gov): remove leading comma in proposal_messages event attribute (fix(x/gov): remove leading comma in proposal_messages event attribute #26353)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.86%. Comparing base (4842dd4) to head (e69da8d).
⚠️ Report is 15 commits behind head on release/v0.54.x.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release/v0.54.x   #26382      +/-   ##
===================================================
+ Coverage            64.83%   64.86%   +0.02%     
===================================================
  Files                  874      874              
  Lines                57559    57559              
===================================================
+ Hits                 37321    37338      +17     
+ Misses               20238    20221      -17     

Files with missing lines	Coverage Δ
x/gov/keeper/proposal.go	83.09% <100.00%> (ø)

... and 3 files with indirect coverage changes

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