KTL-4174 Fix updating timestamp

Author: zwiora

integrations/github/src/test/kotlin/io/klibs/integration/github/GitHubIntegrationKohsukeLibraryGetKlibsIssuesTest.kt

@@ -177,12 +177,16 @@ class GitHubIntegrationKohsukeLibraryGetKlibsIssuesTest {
             mock<GHLabel> { on { it.name } doReturn name }
         }
 
-        return mock {
+        val issue = mock<GHIssue> {
             on { it.number } doReturn number
             on { it.body } doReturn body
             on { it.isPullRequest } doReturn isPullRequest
-            on { it.createdAt} doReturn createdAt
             on { it.labels } doReturn mockedLabels
         }
+
+        // We can't simply put it into the mock structure because Mockito clashes with Kohsuke's hidden bridge methods
+        doAnswer { createdAt }.whenever(issue).getCreatedAt()
+
+        return issue
     }
 }