Updates the Gutenberg ref to include changes that generate both minified and non-minified CSS files during build. Previously, the build only produced a single CSS file (e.g., `style.css`), causing missing asset errors when `SCRIPT_DEBUG` is set to `false`, as Core expects `.min.css` files.
Props peterwilsoncc, dd32, tyxla, jsnajdr, mcsf.
Fixes#64393.
Built from https://develop.svn.wordpress.org/trunk@61446
git-svn-id: http://core.svn.wordpress.org/trunk@60758 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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