[chore] Fix a Swagger warning that only manifests during Go client code generation

[VyrCossont]

Description

Followup to #2698. Found while updating generated code in https://github.com/VyrCossont/slurp:

2024/03/06 09:24:23 validating spec https://raw.githubusercontent.com/superseriousbusiness/gotosocial/main/docs/api/swagger.yaml
2024/03/06 09:24:27 preprocessing spec with option:  minimal flattening
2024/03/06 09:24:27 building a plan for generation
2024/03/06 09:24:27 generation target ./
2024/03/06 09:24:27 planning definitions (found: 67)
2024/03/06 09:24:27 warning: validation minLength (value: 1) not compatible with type [array]. Skipped
2024/03/06 09:24:27 planning operations (found: 126)
2024/03/06 09:24:31 grouping operations into packages (packages: 27)
2024/03/06 09:24:31 operations for package packages "favourites" (found: 1)
2024/03/06 09:24:31 operations for package packages "federation" (found: 3)
2024/03/06 09:24:31 …

I'm not yet sure why go-swagger's validator only catches this while generating Go client code, but meanwhile, this one property should definitely be minItems instead of minLength.

Checklist

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have not leveraged AI to create the proposed changes.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.