Attempting https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/506182 introduced a blocker to editors as it was no longer possible to edit entities that already had the same label and description. Even if this edit is to deliberately make them different. It failed with:
```
{"error":{"code":"modification-failed","info":"Label and description for language code en-gb can not have the same value.","messages":[{"name":"wikibase-validator-label-equals-description","parameters":["en-gb"],"html":{"*":"Label and description for language code en-gb can not have the same value."}}],"*":"See http://default.web.mw.localhost:8080/mediawiki/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes."},"servedby":"66c7ba2ea93a"}
```
**Acceptance Criteria**
Given an entity that have same label and description in a language
When an editor changes the label or description of that language but they are still equal
And saves their changes
Then the save attempt should fail
Given an entity that have same label and description in a language
When an editor changes the label or description of that language so they are not equal
And saves their changes
Then the save attempt should not fail
And the new label and descriptions should be persisted
Given an entity that have same label and description in a language
When an editor do valid changes to labels, descriptions or aliases in **other** languages only (a.k.a the editor didn't touch the language with the equal label/description at all), and do not introduce any equal label/description pairs per language
And saves their changes
Then the save attempt should not fail
And the new label and descriptions should be persisted