Downgraded ElasticSearch to version 8 (#590)

ref [INC-275](https://app.incident.io/ghost/incidents/275)

Added a test to ensure that the major version of ElasticSearch is the
one that we're currently using in production, and won't be
accidentally updated by renovate.

Author: sam-lord

packages/elasticsearch/package.json

@@ -23,7 +23,7 @@
     "posttest": "pnpm run lint"
   },
   "dependencies": {
-    "@elastic/elasticsearch": "9.3.4",
+    "@elastic/elasticsearch": "8.19.1",
     "@tryghost/debug": "workspace:*",
     "split2": "4.2.0"
   },

packages/elasticsearch/test/ElasticSearch.test.js

@@ -1,11 +1,21 @@
 const assert = require('assert/strict');
+const fs = require('fs');
+const path = require('path');
 const sinon = require('sinon');
 const sandbox = sinon.createSandbox();
 
 const { Client } = require('@elastic/elasticsearch');
 const ElasticSearch = require('../index');
 const ElasticSearchBunyan = require('../lib/ElasticSearchBunyan');
 
+const EXPECTED_ELASTICSEARCH_MAJOR = 8;
+const elasticsearchPackage = JSON.parse(
+    fs.readFileSync(
+        path.join(path.dirname(require.resolve('@elastic/elasticsearch')), 'package.json'),
+        'utf8',
+    ),
+);
+
 const testClientConfig = {
     node: 'http://test-elastic-client',
     auth: {
@@ -24,6 +34,15 @@ describe('ElasticSearch', function () {
         sandbox.restore();
     });
 
+    it(`Uses @elastic/elasticsearch v${EXPECTED_ELASTICSEARCH_MAJOR}`, function () {
+        const installedMajor = Number(elasticsearchPackage.version.split('.')[0]);
+        assert.equal(
+            installedMajor,
+            EXPECTED_ELASTICSEARCH_MAJOR,
+            `Expected @elastic/elasticsearch v${EXPECTED_ELASTICSEARCH_MAJOR}, got v${elasticsearchPackage.version}`,
+        );
+    });
+
     it('Processes client configuration', function () {
         const es = new ElasticSearch(testClientConfig);