Force Jest to use exactly one copy of React and ReactDOM

package.json

@@ -202,7 +202,9 @@
     "moduleNameMapper": {
       "\\.(gif|png|svg|ttf|woff2)$": "<rootDir>/node_modules/matrix-react-sdk/__mocks__/imageMock.js",
       "\\$webapp/i18n/languages.json": "<rootDir>/node_modules/matrix-react-sdk/__mocks__/languages.json",
-      "^browser-request$": "<rootDir>/node_modules/matrix-react-sdk/__mocks__/browser-request.js"
+      "^browser-request$": "<rootDir>/node_modules/matrix-react-sdk/__mocks__/browser-request.js",
+      "^react$": "<rootDir>/node_modules/react",
+      "^react-dom$": "<rootDir>/node_modules/react-dom"
     },
     "transformIgnorePatterns": [
       "/node_modules/(?!matrix-js-sdk).+$",