CompatHelper: bump compat for "Documenter" to "0.25"

[github-actions]

This pull request changes the compat entry for the Documenter package from 0.23, 0.24 to 0.23, 0.24, 0.25.

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 #4 into master will decrease coverage by 2.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #4      +/-   ##
==========================================
- Coverage   83.84%   81.57%   -2.28%     
==========================================
  Files          15       15              
  Lines         359      369      +10     
==========================================
  Hits          301      301              
- Misses         58       68      +10     

Impacted Files	Coverage Δ
src/analytic/ezcosz.jl	60.00% <0.00%> (-15.00%)	⬇️
src/analytic/symmetric_quadratic.jl	83.33% <0.00%> (-7.58%)	⬇️
src/analytic/theta_pinch.jl	76.92% <0.00%> (-6.42%)	⬇️
src/analytic/axisymmetric_tokamak_cartesian.jl	68.75% <0.00%> (-4.59%)	⬇️
src/analytic/solovev_quadratic.jl	45.45% <0.00%> (-4.55%)	⬇️
src/analytic/abc.jl	70.58% <0.00%> (-4.42%)	⬇️
src/analytic/axisymmetric_tokamak_cylindrical.jl	80.00% <0.00%> (-3.34%)	⬇️
src/analytic/axisymmetric_tokamak_toroidal.jl	81.48% <0.00%> (-3.14%)	⬇️
src/analytic/solovev.jl	50.00% <0.00%> (-2.64%)	⬇️
src/analytic/solovev_xpoint.jl	45.45% <0.00%> (-2.17%)	⬇️

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