[dotnet] Propagate IWebDriver.GetAttribute obsoletion to WebDriver (#14802)

Author: RenderMichael

dotnet/src/support/Events/EventFiringWebDriver.cs

@@ -1613,6 +1613,7 @@ public void Click()
             /// </summary>
             /// <param name="attributeName">Attribute you wish to get details of</param>
             /// <returns>The attribute's current value or null if the value is not set.</returns>
+            [Obsolete("Use GetDomAttribute(string attributeName) or GetDomProperty(string propertyName). GetAttribute(string attributeName) will be removed in Selenium 6.")]
             public string GetAttribute(string attributeName)
             {
                 string attribute = string.Empty;

dotnet/src/webdriver/WebElement.cs

@@ -411,6 +411,7 @@ public virtual ReadOnlyCollection<IWebElement> FindElements(string mechanism, st
         /// via JavaScript.
         /// </remarks>
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
+        [Obsolete("Use GetDomAttribute(string attributeName) or GetDomProperty(string propertyName). GetAttribute(string attributeName) will be removed in Selenium 6.")]
         public virtual string GetAttribute(string attributeName)
         {
             Response commandResponse = null;