Upgrade `openapi-{schema,spec}-validator` versions

[ngnpope]

I'm not sure whether it was intended that these were not updated or whether it was because caret requirements behave specially for 0.y.z and that was overlooked.

I had to switch openapi_v3_spec_validator to openapi_v30_spec_validator in a couple of places after updating openapi-spec-validator as openapi_v3_spec_validator defaults to openapi_v31_spec_validator there now. I guess we're waiting on #373 for that to be ironed out here.