Update language for xUnit2031 descriptor

src/xunit.analyzers/Utility/Descriptors.xUnit2xxx.cs

@@ -281,10 +281,10 @@ public static partial class Descriptors
  public static DiagnosticDescriptor X2031_AssertSingleShouldUseTwoArgumentCall { get; } =
  Diagnostic(
  "xUnit2031",
- "Do not use single-argument Assert.Single in a filtered collection",
+ "Do not use Where clause with Assert.Single",
  Assertions,
  Warning,
- "Do not use single-argument call to Assert.Single to check for a single item in a filtered collection. Use two-argument call instead."
+ "Do not use a Where clause to filter before calling Assert.Single. Use the overload of Assert.Single that accepts a filtering function."
  );
 
  // Placeholder for rule X2032