ci: add permissions to yml validation workflow (#4678)

As per OpenSSF recommendations, we want to have basic permissions on all our
workflows and the yml checker was missing the line.

Signed-off-by: Terri Oda <terri.oda@intel.com>

.github/workflows/validate-yml.yml

@@ -1,5 +1,7 @@
 name: Validate mismatch_relations.yml
 
+permissions: read-all
+
 on:
   push:
     paths: