Add AutomaticTestableRule conformance to EnumCaseAssociatedValuesLengthRule

[marcelofabri]

Follow up from #2998

[SwiftLintBot]

	1 Warning
⚠️	Please include a CHANGELOG entry to credit yourself! You can find it at CHANGELOG.md.

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* Add AutomaticTestableRule conformance to EnumCaseAssociatedValuesLengthRule.  
  [marcelofabri](https://github.com/marcelofabri)
  [#issue_number](https://github.com/realm/SwiftLint/issues/issue_number)

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