False positive extension_access_modifier with Xcode 11.4

[CraigSiemens]

New Issue Checklist

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

Describe the bug

extension_access_modifier reports a violation when an extension contains a method with an explicit access modifier and a method with an implicit modifier of internal.

Complete output when running SwiftLint, including the stack trace and command used

$ swiftlint 
Loading configuration from '.swiftlint.yml'
Linting Swift files at paths 
Linting 'Test.swift' (1/1)
/Users/craig/Desktop/test/Test.swift:3:1: warning: Extension Access Modifier Violation: Prefer to use extension access modifiers (extension_access_modifier)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version: 0.39.1
• Installation method used: Homebrew
• Paste your configuration file:

opt_in_rules:
  - extension_access_modifier

• Are you using nested configurations? No
  If so, paste their relative paths and respective contents.
• Which Xcode version are you using (check xcodebuild -version)? 11.4
• Do you have a sample that shows the issue? Run echo "[string here]" | swiftlint lint --no-cache --use-stdin --enable-all-rules
  to quickly test if your example is really demonstrating the issue. If your example is more
  complex, you can use swiftlint lint --path [file here] --no-cache --enable-all-rules.

struct Foo {}

// Extension Access Modifier Violation: Prefer to use extension access modifiers (extension_access_modifier)
extension Foo {
    func setup() {}
    public func update() {}
}

[marcelofabri]

Fixed in #3153