The existing actions/checkout@v2 is causing Node v12 deprecation warnings
to be shown in GitHub Actions. v3 uses Node v16, which will stop the
warnings.
IDF v4.4 does not have an official release so for now use the latest
master. Also remove building GENERIC with no options (all the other boards
are no-option builds), to keep CI time reasonable.
Signed-off-by: Damien George <damien@micropython.org>