Do not call API if there is no API URL

CHANGELOG

@@ -28,6 +28,7 @@ v 8.4.0 (unreleased)
   - Ajax filter by message for commits page
 
 v 8.3.3 (unreleased)
+  - Preserve CE behavior with JIRA integration by only calling API if URL is set
   - Get "Merge when build succeeds" to work when commits were pushed to MR target branch while builds were running
   - Fix project transfer e-mail sending incorrect paths in e-mail notification (Stan Hu)
   - Enable "Add key" button when user fills in a proper key (Stan Hu)

app/models/project_services/jira_service.rb

@@ -121,6 +121,7 @@ class JiraService < IssueTrackerService
   end
 
   def test_settings
+    return unless api_url.present?
     result = JiraService.get(
       jira_api_test_url,
       headers: {
@@ -218,6 +219,7 @@ class JiraService < IssueTrackerService
   end
 
   def send_message(url, message)
+    return unless api_url.present?
     result = JiraService.post(
       url,
       body: message,
@@ -243,6 +245,7 @@ class JiraService < IssueTrackerService
   end
 
   def existing_comment?(issue_name, new_comment)
+    return unless api_url.present?
     result = JiraService.get(
       comment_url(issue_name),
       headers: {