Update FormEnctypeNode.php to fix 12824

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12824
| License       | MIT
| Doc PR        | 

I found that in #8731 the semi-colon was actually removed because of a problem with using the sandbox.
Which is properly why this was no longer noticed.

This is the simplest way to fix the syntax error.