ci: Move execution method of tasks into yaml templates
This is done in preparation for making the compute resources for CI
configurable. It also looks cleaner.
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/
20230808021541.7lbzdefvma7qmn3w@awork3.anarazel.de
Backpatch: 15-, where CI support was added