CompatHelper: bump compat for OrdinaryDiffEq to 6, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the OrdinaryDiffEq package from 5.50 to 5.50, 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-commenter]

Codecov Report

Merging #74 (dc07a78) into master (041803a) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   89.51%   89.50%   -0.02%     
==========================================
  Files          10        9       -1     
  Lines         992      991       -1     
==========================================
- Hits          888      887       -1     
  Misses        104      104              

Impacted Files	Coverage Δ
src/NonlinearSchrodinger.jl

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 041803a...dc07a78. Read the comment docs.