Bump react-router from 7.9.5 to 7.12.0 in /packages/pmc

Bumps [react-router](https://github.com/remix-run/react-router/tree/HEAD/packages/react-router) from 7.9.5 to 7.12.0.
- [Release notes](https://github.com/remix-run/react-router/releases)
- [Changelog](https://github.com/remix-run/react-router/blob/main/packages/react-router/CHANGELOG.md)
- [Commits](https://github.com/remix-run/react-router/commits/react-router@7.12.0/packages/react-router)

---
updated-dependencies:
- dependency-name: react-router
  dependency-version: 7.12.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

packages/pmc/package.json

@@ -69,7 +69,7 @@
     "myst-common": "^1.9.3",
     "pmc-utils": "0.3.1",
     "react": "^18.3.1",
-    "react-router": "7.9.5",
+    "react-router": "7.12.0",
     "uuidv7": "^1.0.2",
     "zod": "^4.1.12",
     "zod-form-data": "^3.0.1"