Fix ERA5 native6 fix to handle single monthly-averaged NetCDF files.

[rbeucher]

Description

Modifies the get_frequency function in ERA5 native6 fix to handle case where monthly-averaged data are stored in single NetCDF file (one file per month) and have thus a time dimension length of 1.

Closes #2511

Link to documentation:

---

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[rbeucher]

Hi @schlunma, @valeriupredoi,

Could someone please take a moment to review this for me? Thanks!

R

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.67%. Comparing base (ce8714b) to head (75e8346).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2512   +/-   ##
=======================================
  Coverage   94.66%   94.67%           
=======================================
  Files         251      251           
  Lines       14302    14302           
=======================================
+ Hits        13539    13540    +1     
+ Misses        763      762    -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[valeriupredoi]

looking good @rbeucher - and biy did you have to wait for a review - sorry 🍺 @schlunma @sloosvel maybe we can squeeze this one in 2.12?