meta-schemas: Add a pattern for maintainers emails

The jsonschema package doesn't do anything validation with 'format:
email' because 'it's hard'. For our purposes, the requirements are a bit
simpler. A local, not fully qualified, email address is not accepted so
we can require at least a '@' character is present.

Signed-off-by: Rob Herring (Arm) <[email protected]>

Author: robherring

dtschema/meta-schemas/base.yaml

@@ -39,6 +39,7 @@ properties:
   maintainers:
     type: array
     items:
+      pattern: '@'
       type: string
       format: email