[Yaml] don't override internal PHP constants

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11783 
| License       | MIT
| Doc PR        |
Would it be worth using ``PHP_VERSION_ID > 50400`` instead ? This way, OPCache could optimize it (it will inline the constant value for sure, and it could be smart enough to inline the comparison result as it would compare 2 constants which would then eliminate the useless branch entirely)