Fix INumber.Sign documentation to correctly state return value for zero

Co-authored-by: jeffhandley <[email protected]>

Author: Copilot

xml/System.Numerics/INumber`1.xml

@@ -438,7 +438,7 @@ For <xref:System.Numerics.IFloatingPoint%601> this method matches the IEEE 754:2
       <Docs>
         <param name="value">The value whose sign is to be computed.</param>
         <summary>Computes the sign of a value.</summary>
-        <returns>A positive value if <paramref name="value" /> is positive, <see cref="P:System.Numerics.INumberBase`1.Zero" /> if <paramref name="value" /> is zero, and a negative value if <paramref name="value" /> is negative.</returns>
+        <returns>A positive value if <paramref name="value" /> is positive, <c>0</c> if <paramref name="value" /> is zero, and a negative value if <paramref name="value" /> is negative.</returns>
         <remarks>
           <format type="text/markdown"><![CDATA[