schema: validate schemas against meta-schemas

[albestro]

• schema: required keywords not enforced for spack in config.yaml #252

The idea behind this is to add a CI check that validates schemas against meta schemas, aiming at early catching small errors like #252.

Changelog:

• CI: use pipx to install both uv and check-jsonschema
• CI: use check-jsonschema to validate all schemas (json files) in stackiantor/schema directory

[albestro]

Nice to add:

• do not exit at first fail
• (optional) more concise error message
• if nothing custom is needed (e.g. versioning), evaluate switching to check-jsonschema

[albestro]

The note in previous comment has been fully addressed: switched to check-jsonschema that provides a better error message, and put in a script that accumulates errors from all validation and just errors in the end if at least one validation failed.

See https://github.com/eth-cscs/stackinator/actions/runs/16642216221/job/47094558980 for an example of failure.

stackinator/schema/cache.json
ok -- validation done
stackinator/schema/environments.json
ok -- validation done
stackinator/schema/compilers.json
ok -- validation done
stackinator/schema/config.json
Schema validation errors were encountered.
  stackinator/schema/config.json::$.properties.spack.properties.required: ['repo', 'commit', 'packages'] is not of type 'object', 'boolean'

[albestro]

As soon as #252 gets merged, which fixes the schema reported as error in the previous CI run, this one can be reviewed and merged.

[bcumming]

Thanks, just a few little fixes to stick with using uv for package management.

[bcumming]

Using pipx to install uv is a little bit meta - uv is supposed to be a replacement for pipx.
Instead, you can use uvx to run check-jsonschema.

[bcumming]

Suggested change

	check-jsonschema --check-metaschema $schema
	uvx check-jsonschema --check-metaschema $schema