[met downscaling] Fix for non-hour timesteps in cfmet.downscale.daily

[infotroph]

I think this was a flipped multiply/divide -- the now-replaced 0:(23 * output.dt)/output.dt (which has been there for a looong time!) works when output.dt == 1, but gives too many rows for larger timesteps.

I assume the original intention was to write 0:(23/output.dt)*output.dt, but I replaced it with seq(0, 23, by = output.dt) -- that behaves identically and is a lot clearer to me.

Motivation and Context

Noticed while reviewing #3218

Review Time Estimate

• [ ] Immediately
• [ ] Within one week
• [ ] When possible

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] My name is in the list of CITATION.cff
• [ ] I have updated the CHANGELOG.md.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[infotroph]

Bonus points for adding a unit test!

This one was a poster child for test-driven development: I saw some funny behavior, wrote the test to decide whether it was a bug, and the answer was yes. I wish they were all this easy to test!