build: move system and samples test from Node 10 to Node 12 (#379)
build: move system and samples test from Node 10 to Node 12 (#379)

This PR was generated using Autosynth. :rainbow:

Synth log will be available here:
https://source.cloud.google.com/results/invocations/ba2d388f-b3b2-4ad7-a163-0c6b4d86894f/targets

- [ ] To automatically regenerate this PR, check this box.

Source-Link: https://github.com/googleapis/synthtool/commit/05de3e1e14a0b07eab8b474e669164dbd31f81fb
googleapis/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node