use smaller micromamba_jll rather than huge MKL_jll to test lazy artifacts

[IanButterworth]

Fixes #766

MKL_jll was used to test lazy artifact downloading.

micromamba_jll artifacts are also lazy but a lot smaller (~5-7 MiB) than MKL_jll which is nearly 1GB

This switches over.

https://github.com/JuliaBinaryWrappers/micromamba_jll.jl/blob/main/Artifacts.toml

[codecov]

Codecov Report

Merging #772 (027fb6b) into master (027fb6b) will not change coverage.
The diff coverage is n/a.

❗ Current head 027fb6b differs from pull request most recent head bcbbe65. Consider uploading reports for the commit bcbbe65 to get more accurate results

@@           Coverage Diff           @@
##           master     #772   +/-   ##
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  Coverage   83.08%   83.08%           
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  Files           3        3           
  Lines         662      662           
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  Hits          550      550           
  Misses        112      112           

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[DilumAluthge]

micromamba_jll artifacts are lazy but a lot smaller (~5-7 MiB) than MKL_jll which is nearly 1GB

To provide context for others (like me) that might be confused by this sentence, the MKL_jll artifacts are lazy (https://github.com/JuliaBinaryWrappers/MKL_jll.jl/blob/main/Artifacts.toml).