check that CI is rejecting un-updated schemas

[roedoejet]

No description provided.

[joanise]

2024-04-15 EV dev meeting discussion. By consensus, we agreed that:

• A change to the schemas requires a bump of the minor version number.
  • E.g., once EV 0.1.x is published, and the 0.1 schemas are published on the schema store, a new change to the schemas would immediately bump us to start development on 0.2.x.
  • However, as long as no 0.2.x is published yet, further changes can be made in the main branch, with the schemas updated each time, all to be published together as 0.2.
• Each change that modifies the schemas should run everyvoice update-schemas (this currently requires first removing the contents of everyvoice/.schema/) and commit the results
• This Issue's task is to write a CI check that the above action yields no change, and thus remind the committer to do so if they forgot.