Add Julia v1.6 to ci

[blegat]

If we say that we support it, we should test it

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.72%. Comparing base (5d25d64) to head (3bd2a64).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #323      +/-   ##
==========================================
+ Coverage   88.25%   88.72%   +0.47%     
==========================================
  Files          16       16              
  Lines        1941     1960      +19     
==========================================
+ Hits         1713     1739      +26     
+ Misses        228      221       -7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.