Cloud-init Broken with jsonschema 4.21.0

[holmanb]

Bug report

I got CI working again in #4781, but we really should update our tests and make sure that the behavior that changed isn't something that actually breaks cloud-init.

Steps to reproduce the problem

Run unittests with latest jsonschema.

[TheRealFalcon]

They changed some error messages and our tests were checking for specific error messages:
python-jsonschema/jsonschema@8875c2e
python-jsonschema/jsonschema@a1d4cb3

Given that we'll have to support multiple versions of jsonschema across series, we either need to not check for a specific error message or check that we match either message.

[dermotbradley]

I'm now hitting this issue locally with my testing of Alpine cloud-init packaging (which I use for ongoing cloud-init development) as Alpine updated their py3-jsonschema package to version 4.21.1 last week...

[dermotbradley]

@TheRealFalcon here's a diff of what I had to apply locally to get cloud-init tests passing with the latest py3-jsonschema: https://gist.github.com/dermotbradley/45f2987c9da4d2ad11e8374ba13f4062

I didn't raise a PR as this doesn't cover backwards-compatibility.