Set nullability after using statements

Author: RenderMichael

dotnet/src/webdriver/DefaultFileDetector.cs

@@ -16,10 +16,10 @@
 // limitations under the License.
 // </copyright>
 
-#nullable enable
-
 using System.Diagnostics.CodeAnalysis;
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>

dotnet/src/webdriver/IFileDetector.cs

@@ -16,10 +16,10 @@
 // limitations under the License.
 // </copyright>
 
-#nullable enable
-
 using System.Diagnostics.CodeAnalysis;
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>