Flexbox not working on page floats (Regression in v2.28.0)

[MurakamiShinyu]

Test case: https://gist.githubusercontent.com/MurakamiShinyu/dd49bcd1a882883299bab9d8c256a2c5/raw/page-float-flex.html

Test with Vivliostyle Viewer v2.30.1:
https://vivliostyle.github.io/viewer/v2.30.1/#src=https://gist.githubusercontent.com/MurakamiShinyu/dd49bcd1a882883299bab9d8c256a2c5/raw/page-float-flex.html

Screenshot:

In this result, the "Figure using flexbox" is good but the "Figure using flexbox and page-float" is not good, in which flexbox is not working.

This problem occurs in v2.28.0 and later; it did not occur in v2.27.0 and earlier.

Test with Vivliostyle Viewer v2.27.0:
https://vivliostyle.github.io/viewer/v2.27.0/#src=https://gist.githubusercontent.com/MurakamiShinyu/dd49bcd1a882883299bab9d8c256a2c5/raw/page-float-flex.html

[MurakamiShinyu]

Fixed in PR #1355.

Test: https://vivliostyle-git-fix-issue1354-vivliostyle.vercel.app/#src=https://gist.githubusercontent.com/MurakamiShinyu/dd49bcd1a882883299bab9d8c256a2c5/raw/page-float-flex.html