[YAML] resolve variables in inlined YAML

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11665
| License       | MIT
| Doc PR        | 

#11569 does not resolve variables in inline YAML.
I see, but what i found here is a coding problem, this code should not call array_key_exists with wrong parameters generating a php warning, instead, it should throw a ParseException.