Hugo 0.76.4: One Bug Fix

This is a bug-fix release with a couple of important fixes.

• snap: Install postcss v8 explicitly as it is now a peer dependency e9a7ebaf @anthonyfok
• lang/i18n: Fix for language code case issue with pt-br etc. 50682043 @bep #7804
• Merge branch ‘release-0.76.3’ 49972d07 @bep
• Add merge helper c98132e3 @bep