fix: sortMenusByFrontmatterOrder not been sorted in numerical order but in string order

[Cryolitia]

The behavior inconsistent with documentation:

Sorts the menu items by the order property of the frontmatter. For each folder, sorts the value (number) of the order property in ascending order, or descending order if the sortMenusOrderByDescending option is true. If the value of order is non-numeric or does not exist, order is judged to be 0.

The test samples are also unreasonable. Using 1 2 3 4 as samples will not be able to detect this error.

[jooy2]

Hello! Thank you for your contribution to the project.

As you describe, it should have been sorted a little more clearly based on the values in frontmatter, I missed this point.
I don't see any particular problem with the code, so I'll merge it and release a new version. thanks!

[jooy2]

This change was released in vitepress-sidebar 1.27.1.