Update PhpEngine.php

just a minor phpdoc fix
merged branch janschoenherr/patch-5 (PR #7600)

This PR was submitted for the 2.2 branch but it was merged into the 2.1 branch instead (closes #7600).

Discussion
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[Templating] Update PhpEngine.php

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

just a minor phpdoc fix

Commits
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171b41f Update PhpEngine.php