Upgrade nodejs to version 12

It's what comes with bullseye.

Change-Id: Ib7d77f1564c90c05c85deebf782f214b8cae6191
diff --git a/playbooks/gerrit-setup/pre.yaml b/playbooks/gerrit-setup/pre.yaml
index 2e83666..f89d99d 100644
--- a/playbooks/gerrit-setup/pre.yaml
+++ b/playbooks/gerrit-setup/pre.yaml
@@ -4,6 +4,6 @@
     - ensure-bazelisk
     - ensure-java
     - role: ensure-nodejs
-      node_version: 10
+      node_version: 12
     - install-build-essential
     - prepare-gerrit-repos