fix: Ensure we don't hold onto Mutex when grabbing join tuples

[kszlim]

@ritchie46 fix for the usage we discussed

[codspeed-hq]

CodSpeed Performance Report

Merging #15704 will not alter performance

_{Comparing kszlim:patch-4 (1efa00e) with main (2ac0da2)}

Summary

✅ 22 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.34%. Comparing base (04b00e6) to head (49b8fb4).
Report is 1 commits behind head on main.

❗ Current head 49b8fb4 differs from pull request most recent head 1efa00e. Consider uploading reports for the commit 1efa00e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15704      +/-   ##
==========================================
- Coverage   81.35%   81.34%   -0.01%     
==========================================
  Files        1375     1375              
  Lines      176566   176567       +1     
  Branches     2544     2544              
==========================================
- Hits       143637   143626      -11     
- Misses      32448    32459      +11     
- Partials      481      482       +1     

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