CompatHelper: bump compat for "BSON" to "0.3"

[github-actions]

This pull request changes the compat entry for the BSON package from 0.2.4 to 0.2.4, 0.3.

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]

Codecov Report

Merging #98 (c5bdf0d) into master (2fe36b1) will decrease coverage by 0.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   97.56%   97.23%   -0.33%     
==========================================
  Files           6        6              
  Lines         205      181      -24     
==========================================
- Hits          200      176      -24     
  Misses          5        5              

Impacted Files	Coverage Δ
src/JLSOFile.jl	88.23% <0.00%> (-2.25%)	⬇️
src/file_io.jl	93.75% <0.00%> (-0.59%)	⬇️
src/upgrade.jl	100.00% <0.00%> (ø)
src/metadata.jl	100.00% <0.00%> (ø)
src/serialization.jl	100.00% <0.00%> (ø)

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