fix: enum array when using enumName

[deongroenewald]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

If you create an ApiQuery parameter, which has an enum, enumName and isArray: true, like this:

@ApiQuery({
  name: 'page',
  enum: ['a', 'b', 'c'],
  enumName: 'QueryEnum',
  isArray: true
})

The type in the schema will be array instead of the intended type for the items, e.g. string:

"QueryEnum": {
  "type": "array",
  "enum": ["a", "b", "c"]
}

Issue Number: N/A

What is the new behavior?

It will now generate the correct type for the items schema:

"QueryEnum": {
  "type": "string",
  "enum": ["a", "b", "c"]
}

Does this PR introduce a breaking change?

• Yes
• No

Other information

[kamilmysliwiec]

Duplicate #2870