renamed old P_psi to P_psiA

[pierre-eliep-met]

Goal

Simply fixes #280 by renaming P_psi to P_psiA

Type of change

• Bugfix (non-breaking change which fixes a bug/issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change which reorganizes code)
• Release & Version Update (when cumulative changes justify a release)
• Documentation Update

Checklist

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GitHub checks:

• I have added the appropriate tags, reviewers, projects and linked issues to this PR
• I have checked for conflicts with target branch, and merged/rebased in consequence

Model development checks:

• I have performed a self-review of my own code
• I have checked that my changes do not bring any retrocompatibility issue comparing to MML3-DTG-v3 version
• Existing tests pass (including Metroscopia !).
• I have added/updated tests that prove my development works and does not break anything.

Library checks:

• I have checked in the file explorer that I am not adding duplicate file/folder/package (due to renaming or moving file/package)
• I have checked that the packages I upload are stored as separate files

Documentation checks:

• I have made corresponding changes or additions to the documentation
• I have added corresponding entries to the Changelog

[valentind-met]

What are the consequences on the current models ?

[pierre-eliep-met]

None, this is only renaming start values from the with_start_values models in the examples. Current models already contain the correct naming

[pierre-eliep-met]

I will force merging since since this PR is really a minor changed and it is needed to publish MML3. (benediction from @hvernier 😇 )

[pierre-eliep-met]

okay, just renaming