Stop tests on failure

Since tests take almost 20 minute to run, stopping tests as soon as an
failure occurs will allow for faster iteration locally and also free up
resources in the CI pipeline.

phpunit.xml

@@ -6,7 +6,7 @@
          convertNoticesToExceptions="true"
          convertWarningsToExceptions="true"
          processIsolation="false"
-         stopOnFailure="false"
+         stopOnFailure="true"
 >
     <extensions>
         <extension class="Appwrite\Tests\TestHook" />