Chore: Update what's new URL (#30424)

package.json

@@ -46,7 +46,7 @@
     "ci:test-frontend": "yarn run prettier:check && yarn run typecheck && yarn run lint && yarn run test:ci && yarn grafana-toolkit node-version-check && ./scripts/ci-check-strict.sh"
   },
   "grafana": {
-    "whatsNewUrl": "https://grafana.com/docs/grafana/latest/guides/whats-new-in-v7-3/",
+    "whatsNewUrl": "https://grafana.com/docs/grafana/latest/guides/whats-new-in-v7-4/",
     "releaseNotesUrl": "https://grafana.com/docs/grafana/latest/release-notes/"
   },
   "husky": {