Add check for breaking api changes (#20848)

- update ci-breaking-changes.yaml so it check for api contrat breaks
- check fails properly when removing fix
https://github.com/twentyhq/twenty/pull/20825
- check it turns green again when adding fix back

packages/twenty-server/src/utils/assert.ts

@@ -23,9 +23,6 @@ export const assert: Assert = (condition, message, ErrorType) => {
   }
 };
 
-export const assertNotNull = <T>(item: T): item is NonNullable<T> =>
-  item !== null && item !== undefined;
-
 export const assertNever = (_value: never, message?: string): never => {
   throw new Error(message ?? "Didn't expect to get here.");
 };