Snow season length is 0 if there is 0 snow - fix solar_zenith_angle typo

[aulemahal]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes Number of days can be both nan and 0 #1491 and fixes "parallel" -> "parallelized" #1493
• Tests for the changes have been added (for bug fixes / features)
  • (If applicable) Documentation has been added / updated (for bug fixes / features)
• CHANGES.rst has been updated (with summary of main changes)
  • Link to issue (:issue:number) and pull request (:pull:number) has been added

What kind of change does this PR introduce?

snd_season_length and snw_season_length got implemented with the same check as their *_season_start and *_season_end counter parts, with a mask where : not at_least_n_valid(snw.where(snw > 0), n=1, freq=freq).

However, this means the output is NaN if all inputs are 0. This makes sense in the DOY case (can't a have a start/end date if there's no season), but it doesn't in the "length" case. Instead, I think (as does the issue raiser) an all-0 snow timeseries simply means a season length of 0. Thus, I removed the .where(snw > 0) part of the test for those two indicators.

EDIT: I also slipped in another fix for xc.indices.helpers.cosine_of_solar_zenith_angle. There was a typo in the xr.apply_ufunc call.

Does this PR introduce a breaking change?

Yes because it will change the output of two indicators, but I think this is for the best. The previous behaviour was not documented as such in the doc, I believe the new one is actually more intuitive. No need for a warning, IMO.

[github-actions]

Warning
This Pull Request is coming from a fork and must be manually tagged approved in order to perform additional testing.

[aulemahal]

@Zeitsperre do you know why the coveralls action is still hanging here ?

[Zeitsperre]

Coveralls always expects a hook from GitHub with some stats to compare to. The problem is that because we aren't running all tests, the coverage will always be lower than expected, so the statistic is useless for developers until we build with the approved tag.

Maybe there's a way to send along a skip signal to coveralls when we're only building with Python3.9? I'll look into it.

[aulemahal]

Hum... Ok, but then is that the reason I can't merge ?

[github-actions]

Note
It appears that this Pull Request modifies the main.yml workflow.

On inspection, the XCLIM_TESTDATA_BRANCH environment variable is set to the most recent tag (v2023.9.12).

No further action is required.

[Zeitsperre]

Oh, no, it isn't. For some reason, David's PR review didn't trigger the approved label. Weird.