Fix missing_docs false positives for implicit actor requirements

[ZHUOLIN0928]

Fixes #5422

Summary

• Ignore the compiler-provided unownedExecutor requirement when checking an actor's documented members.
• Keep the exemption limited to a direct actor member with a single unownedExecutor binding.
• Add a non-triggering example for the reported implicit actor conformance case.

Validation

• swift build --disable-sandbox --product swiftlint passed.
• Built SwiftLint with --disable-sourcekit reported no missing_docs violation for the implicit actor example, while a regular struct's undocumented unownedExecutor still produced the expected violations.
• swift test --disable-sandbox --filter MissingDocsRuleTests could not run because the installed CommandLineTools environment cannot resolve XCTest while building SwiftSyntax test support.

[SwiftLintBot]

	19 Messages
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