Avoid tostring in SqlConnectionEncryptOptionConverter if we know value is a string (dotnet#4012)

Author: SimonCropp

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlConnectionEncryptOptionConverter.cs

@@ -36,9 +36,9 @@ public override bool CanConvertTo(ITypeDescriptorContext context, Type sourceTyp
         // Overrides the ConvertFrom method of TypeConverter.
         public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
         {
-            if (value is string)
+            if (value is string s)
             {
-                return SqlConnectionEncryptOption.Parse(value.ToString());
+                return SqlConnectionEncryptOption.Parse(s);
             }
             throw ADP.ConvertFailed(value.GetType(), typeof(SqlConnectionEncryptOption), null);
         }