[dotnet] Deprecate WebElement.GetAttribute() (#14676)

Author: shbenzer

dotnet/src/webdriver/IWebElement.cs

@@ -16,6 +16,7 @@
 // limitations under the License.
 // </copyright>
 
+using System;
 using System.Drawing;
 
 namespace OpenQA.Selenium
@@ -170,6 +171,7 @@ public interface IWebElement : ISearchContext
         /// </list>
         /// </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Thrown when the target element is no longer valid in the document DOM.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.")]
         string GetAttribute(string attributeName);
 
         /// <summary>