chore: Bump mobx from 5.15.7 to 6.1.8

Bumps [mobx](https://github.com/mobxjs/mobx) from 5.15.7 to 6.1.8.
- [Release notes](https://github.com/mobxjs/mobx/releases)
- [Commits](https://github.com/mobxjs/mobx/compare/5.15.7...mobx@6.1.8)

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

packages/gatsby-theme-aio/package.json

@@ -87,7 +87,7 @@
     "gatsby-transformer-remark": "^3.0.0",
     "https-browserify": "^1.0.0",
     "mdx-embed": "^0.0.19",
-    "mobx": "^5.15.7",
+    "mobx": "^6.1.8",
     "postcss": "^8.2.8",
     "preact": "^10.5.12",
     "preact-render-to-string": "^5.1.16",

yarn.lock

@@ -12137,10 +12137,10 @@ mobx-react@^6.2.2:
   dependencies:
     mobx-react-lite "^2.2.0"
 
-mobx@^5.15.7:
-  version "5.15.7"
-  resolved "https://registry.yarnpkg.com/mobx/-/mobx-5.15.7.tgz#b9a5f2b6251f5d96980d13c78e9b5d8d4ce22665"
-  integrity sha512-wyM3FghTkhmC+hQjyPGGFdpehrcX1KOXsDuERhfK2YbJemkUhEB+6wzEN639T21onxlfYBmriA1PFnvxTUhcKw==
+mobx@^6.1.8:
+  version "6.1.8"
+  resolved "https://registry.yarnpkg.com/mobx/-/mobx-6.1.8.tgz#5d03cb76d8f7694dd82bfb2578d886945b66450d"
+  integrity sha512-U4yCvUeh6yKXRwFxm2lyJjXPVekOEar/R8ZKWAXem/3fthJqYflViawfjDAUh7lZEvbKqljC3NT/pSaUKpE+gg==
 
 modify-values@^1.0.0:
   version "1.0.1"