Fix Jira importer immutable cache update

The recent update to make the Jira importer cache update
immutable does not properly work so this commit fixes it.

app/assets/javascripts/jira_import/utils/cache_update.js

@@ -22,7 +22,11 @@ export const addInProgressImportToStore = (store, jiraImportStart, fullPath) =>
     ...queryDetails,
     data: produce(sourceData, draftData => {
       draftData.project.jiraImportStatus = IMPORT_STATE.SCHEDULED; // eslint-disable-line no-param-reassign
-      draftData.project.jiraImports.nodes.push(jiraImportStart.jiraImport);
+      // eslint-disable-next-line no-param-reassign
+      draftData.project.jiraImports.nodes = [
+        ...sourceData.project.jiraImports.nodes,
+        jiraImportStart.jiraImport,
+      ];
     }),
   });
 };