fix: upgrade remark-flexible-containers from 1.0.6 to 1.2.1

Snyk has created this PR to upgrade remark-flexible-containers from 1.0.6 to 1.2.1.

See this package in npm:
remark-flexible-containers

See this project in Snyk:
https://app.snyk.io/org/codes-exe/project/4ecc5cb6-47dd-4c60-b1c6-44734276eb03?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

package-lock.json

@@ -16,7 +16,7 @@
     "mdast-util-to-string": "^4.0.0",
     "rehype-stringify": "^9.0.3",
     "remark": "^14.0.3",
-    "remark-flexible-containers": "^1.0.6",
+    "remark-flexible-containers": "^1.2.1",
     "remark-gfm": "^3.0.1",
     "remark-heading-id": "^1.0.0",
     "remark-preset-lint-markdown-style-guide": "^5.1.3",