optional_enum_case_matching triggers on non-enum switch

New Issue Checklist

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

Describe the bug

The optional_enum_case_matching rule is triggered when switching over an optional struct with cases that are static members of the struct. In these instances, removing the ? on the case results in code that doesn't compile (Xcode 11.1).

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

$ swiftlint lint --use-stdin --enable-all-rules
/// Test struct
public struct Foo: Equatable {
    public static let bar: Foo = .init(foo: "bar")

    public let foo: String
}

/// Test variable
public var something: Foo?

switch something {
case .bar?:
    print("bar")

default:
    print("default")
}
<nopath>:12:10: warning: Optional Enum Case Match Violation: Matching an enum case against an optional enum without '?' is supported on Swift 5.1 and above.  (optional_enum_case_matching)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version (run swiftlint version to be sure)?
  0.38.2
• Installation method used (Homebrew, CocoaPods, building from source, etc)?
  CocoaPods
• Paste your configuration file
  n/a
• Are you using nested configurations?
  If so, paste their relative paths and respective contents.
  n/a
• Which Xcode version are you using (check xcodebuild -version)?
  Xcode 11.1, Build version 11A1027
• 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.
  see above

Reproduce the report with swiftlint lint --use-stdin --enable-all-rules using the provided optional Foo struct example, then trace the optional_enum_case_matching rule's handling of switch cases. Done means the rule no longer reports this non-enum case while continuing to identify valid optional enum-case matches; add regression coverage for the example.