CompatHelper: bump compat for "XLSX" to "0.6"

[github-actions]

This pull request changes the compat entry for the XLSX package from 0.5.8 to 0.5.8, 0.6.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov-io]

Codecov Report

Merging #24 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #24   +/-   ##
=======================================
  Coverage   37.72%   37.72%           
=======================================
  Files           7        7           
  Lines         281      281           
=======================================
  Hits          106      106           
  Misses        175      175

Impacted Files	Coverage Δ
src/use_codebook.jl	97.1% <0%> (ø)	⬆️

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