DEV: Use response.parsed_body in specs (#9615)

Most of it was autofixed with rubocop-discourse 2.1.1.

spec/requests/user_api_keys_controller_spec.rb

@@ -255,7 +255,7 @@ describe UserApiKeysController do
       SiteSetting.min_trust_level_for_user_api_key = 0
       post "/user-api-key.json", params: args
       expect(response.status).not_to eq(302)
-      payload = JSON.parse(response.body)["payload"]
+      payload = response.parsed_body["payload"]
       encrypted = Base64.decode64(payload)
       key = OpenSSL::PKey::RSA.new(private_key)
       parsed = JSON.parse(key.private_decrypt(encrypted))