CompatHelper: bump compat for "ApproxFunBase" to "0.4"

[github-actions]

This pull request changes the compat entry for the ApproxFunBase package from 0.3 to 0.3, 0.4.

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 #733 (34e2863) into master (4463bc2) will increase coverage by 6.11%.
The diff coverage is 47.82%.

@@            Coverage Diff             @@
##           master     #733      +/-   ##
==========================================
+ Coverage   23.79%   29.90%   +6.11%     
==========================================
  Files          15       15              
  Lines         744      846     +102     
==========================================
+ Hits          177      253      +76     
- Misses        567      593      +26     

Impacted Files	Coverage Δ
src/ApproxFun.jl	66.66% <ø> (ø)
src/Extras/fractional.jl	46.91% <ø> (+46.91%)	⬆️
src/Plot/Plot.jl	0.00% <0.00%> (ø)
src/Extras/dualnumbers.jl	10.63% <25.00%> (-2.70%)	⬇️
src/Extras/fftGeneric.jl	20.23% <57.14%> (-0.04%)	⬇️
src/Extras/autodifferentiation.jl	60.00% <100.00%> (+2.30%)	⬆️
src/Extras/sample.jl	72.72% <100.00%> (+1.29%)	⬆️
... and 8 more

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