Fix memory leak in WithLatestFrom

[TTOzzi]

Resolves #139

The withLatestFrom stream has been completed, but it has been confirmed that otherSubscription is remaining and causing memory leaks.
Modified it to call cancel when WithLatestFrom's Subscription is deinitialized.

[codecov]

Codecov Report

Merging #140 (67d8ede) into main (1f6b0df) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 67d8ede differs from pull request most recent head bcda2ca. Consider uploading reports for the commit bcda2ca to get more accurate results

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
+ Coverage   95.45%   95.47%   +0.01%     
==========================================
  Files          72       72              
  Lines        4266     4284      +18     
==========================================
+ Hits         4072     4090      +18     
  Misses        194      194              

Impacted Files	Coverage Δ
Sources/Operators/WithLatestFrom.swift	96.00% <100.00%> (+0.05%)	⬆️
Tests/WithLatestFromTests.swift	98.66% <100.00%> (+0.05%)	⬆️

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[adlerj]

This fix works in the sample project I made

[freak4pc]

Awesome find and fix, thanks for this and for the extra test, too! 🤩