Remove the CI testing for julia 1_4 and 1_5

[lrennels]

No description provided.

[codecov]

Codecov Report

Merging #920 (26b7141) into master (c612e7c) will decrease coverage by 0.41%.
The diff coverage is n/a.

❗ Current head 26b7141 differs from pull request most recent head caf088a. Consider uploading reports for the commit caf088a to get more accurate results

@@            Coverage Diff             @@
##           master     #920      +/-   ##
==========================================
- Coverage   83.73%   83.32%   -0.42%     
==========================================
  Files          40       39       -1     
  Lines        4028     4005      -23     
==========================================
- Hits         3373     3337      -36     
- Misses        655      668      +13     

Flag	Coverage Δ
unittests	83.32% <ø> (-0.42%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/core/delegate.jl	18.75% <0.00%> (-70.54%)	⬇️
src/core/time_arrays.jl	91.84% <0.00%> (-1.59%)	⬇️
src/core/types/core.jl	95.83% <0.00%> (-0.60%)	⬇️
src/Mimi.jl
src/core/defcomp.jl	78.14% <0.00%> (+0.84%)	⬆️

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