fix: Respect join_null argument for semi/anti joins

[ritchie46]

fixes #15685

[codspeed-hq]

CodSpeed Performance Report

Merging #15696 will not alter performance

_{Comparing join_nulls (26eb756) with main (8befcd1)}

Summary

✅ 22 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 96.36364% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 81.34%. Comparing base (8befcd1) to head (26eb756).

Files	Patch %	Lines
...s/src/frame/join/hash_join/single_keys_dispatch.rs	87.50%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15696   +/-   ##
=======================================
  Coverage   81.34%   81.34%           
=======================================
  Files        1375     1375           
  Lines      176532   176558   +26     
  Branches     2544     2544           
=======================================
+ Hits       143604   143627   +23     
- Misses      32445    32450    +5     
+ Partials      483      481    -2     

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