fix: skip invalid code block metadata without key-value pairs

[sarrietav-dev]

Description

This ensures compatibility with transformers like transformerMetaHighlight, which may include metadata without key-value formatting.

Previously, metadata entries without an = would cause [key, value] to be undefined, potentially introducing invalid entries into the map. We now skip such entries to ensure only valid key-value pairs are parsed.

Types of changes

• [X ] Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Documentation Update (if none of the other choices apply)
• Others (any other types not listed above)

Checklist

• I have read the Contributing Guide
• I have added the necessary documentation (if appropriate)
• Breaking Change (fix or feature that would cause existing functionality to not work as expected)

Further comments

Related Issue

[satnaing]

Ah, missed that check.
Thanks!