Bugfix #2575 develop python_convert

[JohnHalleyGotway]

Expected Differences

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

• Describe testing already performed for these changes:
  
  Manually tested this fix on seneca in /d1/projects/METplus/discussions/2214/run.sh:
  The original obs data has range [0,1] and I've configured it with convert(x)=100*x;. Here's a comparison of NetCDF matched pairs output. MET-11.0.1 reports an incorrect range of [0,10000] (after applying the conversion function twice) while the updated MET-main_v11.0 reports the correct range of [0,100] (after applying the conversion function once).

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  
  Review code changes and confirm no GHA diffs are flagged (other than an existing LAEA GRIB2 plot_data_plane one).

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]
  Added to the MET-11.1.0-RC1 release notes.

• Do these changes include sufficient testing updates? [No]
  I decided not to modify any existing unit tests, but could do so if desired.

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [Thurs 6/15/23].
  

Pull Request Checklist

See the METplus Workflow for details.

• Review the source issue metadata (required labels, projects, and milestone).
• Complete the PR definition above.
• Ensure the PR title matches the feature or bugfix branch name.
• Define the PR metadata, as permissions allow.
  Select: Reviewer(s)
  Select: Organization level software support Project or Repository level development cycle Project
  Select: Milestone as the version that will include these changes
• After submitting the PR, select Development issue with the original issue number.
• After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• Close the linked issue and delete your feature or bugfix branch from GitHub.

[DanielAdriaansen]

The code change looks straightforward. My only concern was whether this may be a wider problem, but per the docs here:
https://met.readthedocs.io/en/latest/Users_Guide/config_options.html?highlight=convert(x)#regrid

it looks like convert(x) only applies to dataplanes and not point data or other tools so I think this should squash the bug for all cases.

I also tested (using @JohnHalleyGotway run.sh script on seneca) with MET_PYTHON_EXE set and it appears the change works for that case (and the bug was also present for that case in the old version).

I approve.