Fix typo in comment within SubDBClient test file

Corrected the spelling of "client" in a code comment to improve clarity. This change does not affect functionality but ensures the documentation is precise.

SubDBSharp.UnitTest/SubDBClient.Test.cs

@@ -15,7 +15,7 @@ public async Task TestAvailableLanguages()
         {
             // NOTE: SINCE THE SANDBOX IS ALSO DOWN, USE MOCK API
             // TODO:
-            //  * Use NSubstitue to mock the http clien
+            //  * Use NSubstitue to mock the http client
             var subDbClient = new SubDBClient(GetProductInfo(), ApiUrls.SubDBApiSandBoxUrl);
             var response = await subDbClient.GetAvailableLanguagesAsync();
             Assert.NotNull(response.Body);