duplicate_imports not properly taking @testable into account

[vincentisambart]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

duplicate_imports considers some @testable imports as duplicated even though they are not.

import Foo
@testable import struct Foo.Bar // warning: Duplicate Imports Violation: Imports should be unique (duplicate_imports)

The second import is NOT a duplication. swiftlint --fix will remove it but that breaks the code if the code relied on using some of Foo.Bar's internal methods.

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.55.1
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Mint