Fix comparison for summary option in list fragment

[Natureshadow]

For me, the comparison with boolean true did not work for the following frontmatter:

summary = true

The string comparison works.

[stp-ip]

This is used throughout the code so shouldn't be an issue.
Will keep this open, but won't merge as this fix is more a temporary and local thing. We can't change this boolean to a string especially as we use booleans throughout the code.
Maybe Hugo changed something to make this break. 🤔