Added CI test to ensure i18n strings are extracted out

refs https://github.com/TryGhost/Ghost/issues/15502

- this will test if we have strings that aren't present in the JSON
  files in CI, so we don't miss out on translations

ghost/i18n/i18next-parser.config.js

@@ -10,5 +10,7 @@ module.exports = {
     indentation: 4,
     sort: true,
 
+    failOnUpdate: process.env.CI,
+
     output: 'locales/$LOCALE.json'
 };

ghost/i18n/package.json

@@ -8,7 +8,8 @@
   "scripts": {
     "dev": "echo \"Implement me!\"",
     "test:unit": "NODE_ENV=testing c8 --include index.js --include lib --check-coverage --100  --reporter text --reporter cobertura mocha './test/**/*.test.js'",
-    "test": "yarn test:unit",
+    "test": "yarn test:unit && yarn test:translate",
+    "test:translate": "yarn translate:portal",
     "lint:code": "eslint *.js lib/ --ext .js --cache",
     "lint": "yarn lint:code && yarn lint:test",
     "lint:test": "eslint -c test/.eslintrc.js test/ --ext .js --cache",