strict_fileprivate doesn't support private protocols

[cyril-lepottier]

New Issue Checklist

• Updated SwiftLint to the latest version (0.50.3)
• I searched for existing GitHub issues

Describe the bug

The rule strict_fileprivate triggers an error when using fileprivate on methods from a private protocol.

It was said in #1058, that

"when using Swift 4, since basically it'll make possible to convert all the "acceptable" usages of fileprivate to private".

However, this is not (no longer?) true since the swift compiler requires fileprivate when conforming to private protocol:

Method 'aMethod()' must be declared fileprivate because it matches a requirement in private protocol 'APrivateProtocol'

Environment

• SwiftLint version: 0.50.3
• Installation method used: Homebrew
• Paste your configuration file:

only_rules:
  - strict_fileprivate

• No nested configurations
• Xcode version: 14.1 - Build version: 14B47b
• Sample that shows the issue:

class AClass {
}

extension AClass: APrivateProtocol {

    fileprivate func aMethod() {
    }
}

private protocol APrivateProtocol {

    func aMethod()
}