Bump Testcontainers version to 4.5.0 (#1311)

* Bump Testcontainers version to 4.5.0

The Testcontainers dependency Docker.DotNet was bumped to 3.128.1 and is not binary compatible with previous version.
When a user has a direct dependency on Testcontainers 4.5.0, WireMock.Net.Testcontainers fails with :

System.MissingMethodException : Method not found: 'Docker.DotNet.DockerClient Docker.DotNet.DockerClientConfiguration.CreateClient(System.Version)'

* Bump System.Net.Http.Json version to 8.0.1

Minimum required version for Testcontainers 4.5.0

* Do not dispose null container

test/WireMock.Net.Tests/Testcontainers/TestcontainersTests.cs

@@ -123,7 +123,11 @@ public partial class TestcontainersTests
         }
         finally
         {
-            await wireMockContainer.StopAsync();
+            // Stop the container
+            if(wireMockContainer is not null)
+            {
+                await wireMockContainer.StopAsync();
+            }
         }
     }
 }