make pre-commit broke, fix and add .cirrus.yml test it's still sane

[anarazel]

$ make pre-commit 
[...]
packer validate \
  -only "vanilla.*" \
  -var-file=packer/netbsd.pkrvars.hcl \
  -var gcp_project=pg-ci-images-dev \
  -var "image_date=2023-06t12-09-28" \
  -var "image_name=netbsd-vanilla" \
  -var "bucket=somebucket" \
  packer/netbsd_openbsd.pkr.hcl
Error: Unset variable "version"

A used variable must be set or have a default value; see
https://packer.io/docs/templates/hcl_templates/syntax for details.


make: *** [Makefile:11: pre-commit] Error 1

I think a sanity-check task run before all the others, which for now just does make pre-commit, would be good.