change shebang in update_headers to use python-jl instead of python3

[sevyharris]

Motivation or Problem

The script to automatically update the LICENSE header at the top of all files uses python3 instead of python-jl. This script is run when generating new binaries.

Description of Changes

Changed the shebang in the utilities.py:update_headers function to use python-jl instead of python3

[codecov[bot]]

Codecov Report

Merging #2310 (aaacd6a) into main (7f26746) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2310   +/-   ##
=======================================
  Coverage   48.24%   48.24%           
=======================================
  Files         110      110           
  Lines       30612    30612           
  Branches     7982     7982           
=======================================
  Hits        14769    14769           
  Misses      14298    14298           
  Partials     1545     1545           

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[JacksonBurns]

Superseded by #2444