project: fix onNext scheduling in ConcurrentAccessRegulator

[twittemb]

Description

This PR fixes a potential issue where the onNext function could be called in non deterministic order.

Checklist

• [x] this PR is based on the main branch and is up-to-date, if not please rebase your branch on the top of main
• [x] the commits inside this PR have explicit commit messages
• [x] unit tests cover the new feature or the bug fix
• [x] the feature is documented in the README.md if it makes sense
• [x] the CHANGELOG is up-to-date

[codecov-commenter]

Codecov Report

Merging #11 (6081b19) into main (aae817b) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   97.32%   97.32%   -0.01%     
==========================================
  Files          44       44              
  Lines        2243     2240       -3     
==========================================
- Hits         2183     2180       -3     
  Misses         60       60              

Impacted Files	Coverage Δ
Sources/Internal/ConcurrentAccessRegulator.swift	100.00% <100.00%> (ø)
...sts/AsyncSequences/AsyncSequences+MergeTests.swift	97.36% <100.00%> (-0.06%)	:arrow_down:

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