[TwigBundle] fixed wrong rebase in #7375

When rebasing on master, `twig.loader` has not been renamed to `twig.loader.filesystem`.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7375