chore: update pinia from 2.2.2 to 2.2.6

v2.2.6 fixed bug where `shouldHydrate()` is not exported that breaks `pnpm build`
(ref. vuejs/pinia#2798)

Author: shuuji3

package.json

@@ -87,7 +87,7 @@
     "node-emoji": "^2.1.3",
     "nuxt-security": "^2.0.0",
     "page-lifecycle": "^0.1.2",
-    "pinia": "^2.2.2",
+    "pinia": "^2.2.6",
     "postcss-nested": "^7.0.0",
     "prosemirror-highlight": "^0.9.0",
     "rollup-plugin-node-polyfills": "^0.2.1",