bump to Julia 1.6

[dpo]

No description provided.

[tmigot]

Thanks! The CompatHelper.yml and .cirrus files also need to be updated for this.

[codecov]

Codecov Report

Merging #290 (4743a8d) into main (4743a8d) will not change coverage.
The diff coverage is n/a.

❗ Current head 4743a8d differs from pull request most recent head 6f45b99. Consider uploading reports for the commit 6f45b99 to get more accurate results

@@           Coverage Diff           @@
##             main     #290   +/-   ##
=======================================
  Coverage   86.63%   86.63%           
=======================================
  Files           5        5           
  Lines         711      711           
=======================================
  Hits          616      616           
  Misses         95       95           

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[dpo]

Thanks. Done.