Prints help message when I pass a dash symbol even quoted

It prints a help message when I pass a dash symbol even quoted.

**ArgumentParser version:** `0.4.3`
**Swift version:** Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55) Target: x86_64-apple-darwin20.5.0

### Checklist
- [x] If possible, I've reproduced the issue using the `main` branch of this package
- [x] I've searched for [existing GitHub issues](https://github.com/apple/swift-argument-parser/issues)

### Steps to Reproduce

[Here](https://github.com/griffin-stewie/my_echo) is my sample project to test.

Pass double-quoted string as an argument.

### Expected behavior

`my_echo "- [Apple](https://apple.com)"` → `- [Apple](https://apple.com)`

### Actual behavior

It prints the help message of this command.

Start by reproducing the behavior in the linked my_echo sample project with the quoted Markdown-style argument, then trace how swift-argument-parser handles arguments beginning with a dash. Done means the quoted value is passed through as a literal argument instead of causing the command's help message to print.

Written by the indexing model from the issue text.