Fix bug in Container Scanning report remediations

- ContainerScanningVulnerability was missing two
  required fields for remediations to work
  properly `target_branch` and `remediations`

changelogs/unreleased/fix-container-scanning-remediation-bug.yml

+---
+title: Fix bug in Container Scanning report remediations
+merge_request: 21980
+author:
+type: fixed

ee/lib/gitlab/vulnerabilities/container_scanning_vulnerability.rb

@@ -9,6 +9,8 @@ module Gitlab
         severity
         identifiers
         links
+        remediations
+        target_branch
       ].each do |method_name|
         define_method(method_name) do
           @data[method_name]

ee/spec/lib/gitlab/vulnerabilities/container_scanning_vulnerability_spec.rb

@@ -22,7 +22,7 @@ describe Gitlab::Vulnerabilities::ContainerScanningVulnerability do
     let(:vulnerability) { described_class.new(data) }
 
     where(:getter) do
-      %i[severity confidence identifiers links]
+      %i[severity confidence identifiers links target_branch remediations]
     end
 
     with_them do