fix: incorrect arg index in synthetic event

[hstove]

In #4329 (just merged) one of the synthetic events used an incorrect arg index in the print for stack-stx.

I also noticed that stack-aggregation-increase and stack-aggregation-commit have diverged argument signatures - -increase's third arg is reward-cycle-index, whereas -commit's third arg is signer-key. I've made a separate match branch to reflect this change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (74e3ced) 83.39% compared to head (827d4d2) 73.76%.
Report is 1 commits behind head on next.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #4332      +/-   ##
==========================================
- Coverage   83.39%   73.76%   -9.63%     
==========================================
  Files         435      435              
  Lines      309254   309278      +24     
==========================================
- Hits       257892   228136   -29756     
- Misses      51362    81142   +29780     

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[zone117x]

Thanks @hstove!