Fix handling of --- separator inside code-blocks

[alvarobartt]

Description

Apparently the doc-builder does not handle well the --- separators within a YAML code-block when rendering / building the MDX files out of the MD files.

For context, the --- is being used to split the Kubernetes Deployment from the Service in a Kubernetes manifest, I made the doc-builder action pass with this change, so assuming that there's an issue on handling the --- inside a code-block.

Here's the detailed error in the CI in case that's helpful, thanks in advance 🤗