Make schemata check workflow always check for diff

I would like to see the effect on schema (https://github.com/dandi/dandi-schema/blob/master/.github/workflows/test-schema.yml) for every PR to the base (`master`) branch unless it has 'release' label -- then to the prior release (as what it does now I believe). It should not fail regardless as we do allow for changes to schema to be merged, but not released.