ci: improve image-manifest reliability (#981)

diff --git a/Jenkinsfile b/Jenkinsfile
index 1ec8dbf..074a060 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -45,35 +45,21 @@
             }
           }
         }
-
-        stage('image-manifest') {
-          agent {
-            label 'earthly-2c-4g'
-          }
-
-          steps {
-            sh 'earthly +lint.image-manifest'
-          }
-        }
       }
     }
 
     stage('unit') {
-      parallel {
-        stage('go') {
-          agent {
-            label 'earthly-2c-4g'
-          }
+      agent {
+        label 'earthly-2c-4g'
+      }
 
-          steps {
-            sh 'earthly --output +unit.go'
-          }
+      steps {
+        sh 'earthly --output +unit.go'
+      }
 
-          post {
-            always {
-              junit 'junit-go.xml'
-            }
-          }
+      post {
+        always {
+          junit 'junit-go.xml'
         }
       }
     }