test: Set Jest environment to "node" for all server tests

packages/core/jest.config.js

@@ -21,4 +21,5 @@ module.exports = {
             },
         },
     },
+    testEnvironment: 'node',
 };

packages/email-plugin/jest.config.js

@@ -21,4 +21,5 @@ module.exports = {
             },
         },
     },
+    testEnvironment: 'node',
 };