CompatHelper: bump compat for CUDA in [weakdeps] to 6, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the CUDA package from 4, 5 to 4, 5, 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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.22%. Comparing base (8f17bfb) to head (935bdd4).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #587   +/-   ##
=======================================
  Coverage   89.22%   89.22%           
=======================================
  Files          89       89           
  Lines        5855     5855           
=======================================
  Hits         5224     5224           
  Misses        631      631           

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[GiggleLiu]

Current registry/release evidence supports considering CUDA 6.3.1: CUDA 6.0 describes the package split as the reason for the cautious major bump and says no intentional breaking API changes. This PR’s exact head 935bdd462187d0cde9a8bd6ab4dbbf064228388a only widens the root weak-dependency compat, however; ext/CuYao/test/Project.toml still restricts CUDA to 4, 5, and the passing CPU CI jobs do not exercise the CUDA extension on a GPU. I am leaving it open rather than treating those checks as CUDA 6 validation. A qualifying update should widen the test environment to 6 and run the CuYao extension suite on CUDA 6 (or document equivalent GPU CI evidence).