Update XsltArgumentList.xml

[ericamick]

As written, the documentation currently suggests only one parameter per namespace is allowed. It should be one parameter with a given name per namespace.

Summary

Make clear that a duplicate name in the same namespace throws the exception.

Fixes #Issue_Number (if available)

[opbld33]

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[opbld33]

Docs Build status updates of commit 0eb0d49:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Xml.Xsl/XsltArgumentList.xml	✅Succeeded	View

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[buyaa-n]

I think it meant it already has a parameter associated with the given name

Suggested change

	The <paramref name="namespaceUri" /> already has a parameter called <paramref name="name" /> associated with it.</exception>
	The <paramref name="namespaceUri" /> already has a parameter associated with the <paramref name="name" />.</exception>