DRIVERS-3106 revise expected error (#1818)

The legacy test used `errorContains`. The migrated unified test used `isClientError` (copying existing patterns in unified tests). The expected error may come from mongocryptd and not be considered a client error. Revert to using `errorContains`.

Author: kevinAlbs

source/client-side-encryption/tests/unified/localSchema.json

@@ -99,4 +99,5 @@ tests:
         arguments:
           document: &doc0 { _id: 1, encrypted_string: "string0" }
         expectError:
-          isClientError: true
+          isError: true
+          errorContains: "JSON schema keyword 'required' is only allowed with a remote schema"