Casting of literals is done by Calcite, except for strings

[nils-braun]

This PR fixes an issue with occurs due to this

[codecov-commenter]

Codecov Report

Merging #178 (595efae) into main (e065161) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #178   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           57        57           
  Lines         2207      2209    +2     
  Branches       302       303    +1     
=========================================
+ Hits          2207      2209    +2     

Impacted Files	Coverage Δ
dask_sql/physical/rex/core/call.py	100.00% <100.00%> (ø)

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