Fix dast report parsing regression

This regression was caused by changes in zaproxy

ee/changelogs/unreleased/61264-dast-report-error.yml

+---
+title: Fix dast report parsing regression caused by change in zaproxy
+merge_request: 13789
+author:
+type: fixed

ee/lib/gitlab/ci/parsers/security/dast.rb

@@ -25,7 +25,7 @@ module Gitlab
           end
 
           def extract_vulnerabilities_from(data)
-            site = data['site']
+            site = data['site'].first
             results = []
 
             if site

ee/spec/finders/security/pipeline_vulnerabilities_finder_spec.rb

@@ -18,7 +18,7 @@ describe Security::PipelineVulnerabilitiesFinder do
     set(:artifact_sast) { create(:ee_ci_job_artifact, :sast, job: build_sast, project: project) }
 
     let(:cs_count) { read_fixture(artifact_cs)['unapproved'].count }
-    let(:dast_count) { read_fixture(artifact_dast).dig('site', 'alerts').first['instances'].count }
+    let(:dast_count) { read_fixture(artifact_dast)['site'].first['alerts'].first['instances'].count }
     let(:ds_count) { read_fixture(artifact_ds)['vulnerabilities'].count }
     let(:sast_count) { read_fixture(artifact_sast)['vulnerabilities'].count }
 

ee/spec/lib/gitlab/ci/parsers/security/formatters/dast_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 describe Gitlab::Ci::Parsers::Security::Formatters::Dast do
   let(:formatter) { described_class.new(file_vulnerability) }
-  let(:file_vulnerability) { parsed_report['site']['alerts'][0] }
+  let(:file_vulnerability) { parsed_report['site'].first['alerts'][0] }
 
   let(:parsed_report) do
     JSON.parse!(

spec/fixtures/security-reports/master/gl-dast-report.json

 {
-  "site": {
+  "site": [
+    {
       "alerts": [
         {
           "sourceid": "3",
@@ -34,7 +35,8 @@
       "@port": "80",
       "@host": "bikebilly-spring-auto-devops-review-feature-br-3y2gpb.35.192.176.43.xip.io",
       "@name": "http://bikebilly-spring-auto-devops-review-feature-br-3y2gpb.35.192.176.43.xip.io"
-  },
+    }
+  ],
   "@generated": "Fri, 13 Apr 2018 09:22:01",
   "@version": "2.7.0"
 }