fix: Fix projection pushdown bug in IEJOINS

[ritchie46]

fixes #19005

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.87%. Comparing base (e402e70) to head (2d80df4).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/ir/format.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19015   +/-   ##
=======================================
  Coverage   79.87%   79.87%           
=======================================
  Files        1524     1524           
  Lines      207653   207710   +57     
  Branches     2905     2906    +1     
=======================================
+ Hits       165857   165913   +56     
  Misses      41248    41248           
- Partials      548      549    +1     

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