[Process] Inherit the error_reporting from parent

There are several builds failing due to the new E_DEPRECATED_USER messages. This is also an issue in the functional tests. The problem is that the PhpProcess started to run the functional test does not inherit the error_reporting setting from the parent.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | somewhat
| Deprecations? | yes
| Tests pass?   | no (but broken upstream)
| Fixed tickets | 
| License       | MIT
| Doc PR        | 


Relates #12623
Relates #12705