feat(test): try calling .dispose() x2 in emitter

[jsjoeio]

This adds a couple lines to hit 100% test coverage for emitter.ts by ensuring that our logic works when trying to dispose of a callback more than once.

Fixes N/A

[codecov]

Codecov Report

Merging #3713 (f3c4dcd) into main (58514c4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #3713   +/-   ##
=======================================
  Coverage   61.55%   61.55%           
=======================================
  Files          35       35           
  Lines        1813     1813           
  Branches      365      365           
=======================================
  Hits         1116     1116           
  Misses        588      588           
  Partials      109      109           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 58514c4...f3c4dcd. Read the comment docs.