fix: Block predicate pushdown on equality that are use in join

[ritchie46]

fixes #15038

[codecov]

Codecov Report

Attention: Patch coverage is 85.07463% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 81.00%. Comparing base (82932c6) to head (4b4e466).
Report is 5 commits behind head on main.

Files	Patch %	Lines
crates/polars-plan/src/utils.rs	44.44%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15055      +/-   ##
==========================================
- Coverage   81.01%   81.00%   -0.01%     
==========================================
  Files        1338     1338              
  Lines      173595   173673      +78     
  Branches     2461     2461              
==========================================
+ Hits       140635   140682      +47     
- Misses      32490    32521      +31     
  Partials      470      470              

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[exyi]

Thank you!