Bump vue-i18n from 8.26.7 to 8.26.8 in /frontend

Bumps [vue-i18n](https://github.com/kazupon/vue-i18n) from 8.26.7 to 8.26.8.
- [Release notes](https://github.com/kazupon/vue-i18n/releases)
- [Changelog](https://github.com/kazupon/vue-i18n/blob/v8.x/CHANGELOG.md)
- [Commits](https://github.com/kazupon/vue-i18n/compare/v8.26.7...v8.26.8)

---
updated-dependencies:
- dependency-name: vue-i18n
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

frontend/package.json

@@ -15,7 +15,7 @@
     "socket.io-client": "^4.2.0",
     "vue": "^2.6.14",
     "vue-clipboard2": "^0.3.3",
-    "vue-i18n": "^8.26.7",
+    "vue-i18n": "^8.26.8",
     "vue-router": "^3.5.3",
     "vue-socket.io": "^3.0.10"
   },