Ignore OkHttpClientProviderTest test suite. (Graylog2#7799)

The `OkHttpClientProviderTest` test suite was producing test failures
every now and then, requiring to restart the build unnecessarily.

This change is disabling this specific test suite until someone has time
to fix it.

graylog2-server/src/test/java/org/graylog2/shared/bindings/providers/OkHttpClientProviderTest.java

@@ -37,6 +37,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+@Ignore
 public class OkHttpClientProviderTest {
     private final MockWebServer server = new MockWebServer();