* Simplify extraction of zip files in setup.sh
Refactor unzip command to directly extract to target directory.
By keeping the /flutter directory from inside the archive, we avoid having to use a temp directory and move afterwards.
* fix: checkout specific version on main/master
Something with the globing seems not work but not sure exactly. Now using a simple way of ensure that the target folder never exists when calling `mv` so that it behaves as a rename instead of a move into. The folder still needs to be created first so that parent folders (in case of a custom cache path) are created.
Export `PUB_CACHE` if it is not configured before calling the action.
This ensures that flutter and dart use the same cache.
It also enables other tools to use this official Dart env variable.
Peter Leibiger