Should we pin the dart version in the CI build?

[psigen]

It seems a bit weird that all our dart-6.3 branches will start to fail once the dart PPA is upgraded to dart-6.4.

Should we somehow be specifying a major-minor version when we install the dart version such that we will be testing against the latest branch-matched version of dart (e.g. dart 6.3.X for dartpy/dart-6.3?

dartpy/ci/install_linux.sh

Line 6 in 1838ea2

sudo apt-get install libdart6-all-dev -y