chore: add resize observer mock

frontend/apps/remark42/app/__mocks__/resize-observer.ts

@@ -0,0 +1,11 @@
+global.ResizeObserver = class ResizeObserver {
+  observe() {
+    // do nothing
+  }
+  unobserve() {
+    // do nothing
+  }
+  disconnect() {
+    // do nothing
+  }
+};

frontend/apps/remark42/jest.config.ts

@@ -33,6 +33,7 @@ const config: Config = {
   setupFilesAfterEnv: [
     '<rootDir>/app/__mocks__/fetch.ts',
     '<rootDir>/app/__mocks__/localstorage.ts',
+    '<rootDir>/app/__mocks__/resize-observer.ts',
     '<rootDir>/app/__stubs__/remark-config.ts',
     '<rootDir>/app/__stubs__/static-config.ts',
   ],