lint: add unnecessary conversions linter to automated PR advice

[cce]

Summary

This adds the unconvert linter to the .golangci-warnings.yml configuration, which is used by Github Actions & reviewdog to provide automated advice on new lines added that provides linter output, but does not block a PR.

Test Plan

No change besides linter settings.

[codecov]

Codecov Report

Merging #4710 (c599689) into master (ad08f74) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4710      +/-   ##
==========================================
- Coverage   54.49%   54.42%   -0.07%     
==========================================
  Files         407      407              
  Lines       52389    52389              
==========================================
- Hits        28548    28513      -35     
- Misses      21455    21481      +26     
- Partials     2386     2395       +9     

Impacted Files	Coverage Δ
ledger/roundlru.go	90.56% <0.00%> (-5.67%)	⬇️
ledger/blockqueue.go	84.48% <0.00%> (-4.03%)	⬇️
agreement/cryptoVerifier.go	67.60% <0.00%> (-2.12%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
network/wsPeer.go	66.50% <0.00%> (-1.95%)	⬇️
data/transactions/verify/txn.go	76.19% <0.00%> (-0.96%)	⬇️
ledger/catchpointtracker.go	62.10% <0.00%> (-0.79%)	⬇️
ledger/testing/randomAccounts.go	55.59% <0.00%> (-0.63%)	⬇️
ledger/acctupdates.go	69.59% <0.00%> (-0.60%)	⬇️
network/wsNetwork.go	65.34% <0.00%> (-0.19%)	⬇️
... and 3 more

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[michaeldiamant]

@cce Seems reasonable to me.

I'd also be on-board to make unnecessary conversions an error. It's possible an unnecessary conversion becomes necessary through various future changes. Depending on the situation, a conversion may not be desired behavior.

[cce]

Sure! If you want to do that it is a nice soothing sudoku-like game to go in and fix them all and get them lint clean in another PR.. I had intended to use the warning-level linter for introducing potentially controversial linter opinions like this