Bump @storybook/server from 6.3.12 to 6.4.8

Bumps [@storybook/server](https://github.com/storybookjs/storybook/tree/HEAD/app/server) from 6.3.12 to 6.4.8.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/next/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v6.4.8/app/server)

---
updated-dependencies:
- dependency-name: "@storybook/server"
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -16,7 +16,7 @@
   "devDependencies": {
     "@storybook/addon-controls": "^6.4.1",
     "@storybook/addon-docs": "^6.4.3",
-    "@storybook/server": "^6.3.12",
+    "@storybook/server": "^6.4.8",
     "jasmine-core": "~2.4.1",
     "jest": "^27.4.3",
     "karma": "~6.3.9",