Add 1.6 to CI

[odow]

A PR to track fixes for 1.6. Tests fail at present.

[codecov]

Codecov Report

Merging #60 (3458522) into master (a627628) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #60   +/-   ##
=======================================
  Coverage   85.26%   85.26%           
=======================================
  Files          19       19           
  Lines        1344     1344           
=======================================
  Hits         1146     1146           
  Misses        198      198           

Impacted Files	Coverage Δ
src/rewrite.jl	90.24% <100.00%> (ø)

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[odow]

Current failure is caused by: JuliaLang/julia#37065. A fix is proposed: JuliaLang/julia#38250

TODO:

• [ ] retest when 38250 is merged

Actually, it may just be because we need to define ndims(::DummyBigInt)

[odow]

Tests pass on Julia 1.6, but since Github actions are missing allow-failure, I commented out so we can merge and tag a new release. I don't think we need to test nightly permanently.

[blegat]

I commented out so we can merge and tag a new release. I don't think we need to test nightly permanently.

The good thing is that the different CI runs are in separate checks so we can easily see if only nightly is failing.