Content collection frontmatter invalid.

Example error message:
Could not parse frontmatter in blog → post.md
“title” is required.
“date” must be a valid date. (E06002)

A Markdown document’s frontmatter in src/content/ does not match its collection schema. Make sure that all required fields are present, and that all fields are of the correct type. You can check against the collection schema in your src/content/config.* file. See the Content collections documentation for more information.