When `IgnoreUnknownArguments` is true, do not assume any single-dash argument matches a correlating short character option

Currently, Tokenizer will assume a match for a short option when it encounters a single-dash argument, when the first character matches. This is unexpected when `IgnoreUnknownArguments` is set to true--since it should ignore unknown arguments.

https://github.com/commandlineparser/commandline/blob/b0b0ec9f5470bacc0823c013a599ba3b4e115900/src/CommandLine/Core/Tokenizer.cs#L172-L183

Review src/CommandLine/Core/Tokenizer.cs around lines 172-183 and trace how single-dash arguments are matched when IgnoreUnknownArguments is true. Confirm the change by checking that an unknown single-dash argument is ignored rather than correlated to a short option, while valid short options retain their behavior.

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