It used to be installed as a dependency of some other package, but
stopped doing lately, which causes qtbase to build without zstd
support.
This change explicitly installs the libzstd-dev package to prevent
this from happening again.
Pick-to: 6.7 6.8
Fixes: QTBUG-124787
Fixes: QTBUG-127644
Change-Id: I72793ed96ef39ec07244079c51efe17ae1f9af66
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>