webpack-jumpstart.yml: use node:14
webpack-jumpstart.yml: use node:14

This is already precached on the GitHub runner images, so we can save
the time of having to download it.  We only avoided it before in order
to dodge a bug in an old version of git, which we now have a workaround
for.

martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit