Twig: Lazy loaded extensions example does not work in twig<1.35

[mhujer]

Documentation states:

New in version 1.26: Support for lazy-loaded extensions was introduced in Twig 1.26.

However the interface Twig\Extension\RuntimeExtensionInterface which is included in the example is not available until Twig 1.35 (twigphp/Twig@6f08f57)

[javiereguiluz]

@mhujer great catch! Thanks a lot for reporting this bug. We're fixing it in #12766.