Fix ci.json: Remove Nesting from Secrets Rule

Remove Additional Object Wrapper from Secrets Field.

Reference: https://docs.gitlab.com/ee/ci/yaml/#secrets
Documentation: https://docs.gitlab.com/ee/ci/secretsSigned-off-by: Progyan Bhattacharya <bprogyan@gmail.com>
Changelog: fixed

app/assets/javascripts/editor/schema/ci.json

@@ -421,8 +421,6 @@
     "secrets": {
       "type": "object",
       "description": "Defines secrets to be injected as environment variables",
-      "additionalProperties": {
-        "type": "object",
       "additionalProperties": {
         "type": "object",
         "description": "Environment variable name",
@@ -454,7 +452,6 @@
         },
         "required": ["vault"]
       }
-      }
     },
     "before_script": {
       "type": "array",