[bug][minor] Improper markdown highlighting in nested nodes

[Varun0157]

I am developing an extension that allows users to create and document API requests.

I noticed that on attempting to syntactically highlight markdown in nested nodes, a lot of the text (beyond the first line is what I've noticed) gets treated as regular text, regardless of whether it is a header, bullet point etc. The example will make it easier to understand.

Minimum reproducible example:

key:
  doc: | # markdown
    # header // highlighted
    content
    # header // not highlighted
    content

Another example:

• The extension works correctly if the doc node is not nested.
• In general, the issue seems to occur if the text block starts with any kind of header.
• I have the RedHat YAML extension installed, but I doubt it is interfering because this does not work without it either.
• The textmate scope of the second header in the minimum reproducible example does not denote it as a header.

For a larger example, you may try out your extension on this file.

VSCode version: 1.85.1