Pdct 981/admin api if language idempotent language is removed from document

[katybaulch]

Description

When updating a document, the user language was being correctly passed to the API - but if the language was idempotent the API was setting the user language as None in the database.

This PR fixes that bug 🐛

Proposed version

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Type of change

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• Bug fix
• New feature
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How Has This Been Tested?

Have updated update document tests to make sure we are only testing one thing edge case test, as the edge case was not being tested as we were always changing all of the fields in each test. I think we need to review the slug tests however, as I'm not confident that they're working as expected anymore (ticket for doing).

Reviewer Checklist

• The PR represents a single feature (small drive-by fixes are also ok)
• The PR includes tests that are sufficient for the level of risk
• The code is sufficiently commented, particularly in hard-to-understand areas
• Any required documentation updates have been made
• Any TODOs added are captured in future tickets
• No FIXMEs remain

[linear]

PDCT-981 Admin API: If language idempotent, language is removed from document

[diversemix]

Great nice tests too!