$DRONE_BUILD_STARTED not guaranteed to be same between "steps:" and "services:" containers

[kingphil]

After seeing a few Drone CI runs spin and then fail after an hour, I added a basic sanity check on the value of $DRONE_BUILD_STARTED (i.e. - echo sanity - $${DRONE_BUILD_STARTED})

In one run,
k3dsvc: sanity - 1669820814
test: sanity - 1669820815

While the k3d service is healthy, and the kubeconfig is in place, the "test" step is looking for the wrong filename indefinitely.

Suggested resolution: as these are ephemeral environments, we can use a hard-coded filename (e.g. kubeconfig.yaml).