chore: Pin Storybook CLI to v6 for extract docs script [skip release] (…

…#2657)

Fixes: #2656

`npx` is installing the latest version of `sb` (v8) by default, but this requires us to bump to Node 18, which we're not quite ready to do. This should pin it to 6.5.9 to match our other Storybook deps until we're ready to upgrade.

Dependencies, Codemods, and Tokens -->

[category:Infrastructure]

.github/workflows/canary.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Build Storybook
         run: |
           yarn build-storybook --quiet
-          npx sb extract docs docs/stories.json
+          npx sb@6.5.9 extract docs docs/stories.json
 
       ## Build for packaging.
       - name: Build