fix: fixtures/concurrent/time-slicing/package.json & fixtures/concurrent/time-slicing/yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-IP-12704893
- https://snyk.io/vuln/SNYK-JS-IP-12761655

Author: snyk-bot

fixtures/concurrent/time-slicing/package.json

@@ -7,7 +7,7 @@
     "react": "0.0.0-experimental-269dd6ec5",
     "react-dom": "0.0.0-experimental-269dd6ec5",
     "react-markdown": "^3.2.0",
-    "react-scripts": "^1.1.4",
+    "react-scripts": "^5.0.0",
     "victory": "^0.25.6"
   },
   "scripts": {