[Sync EN] singleton.xml: remove extra "an" before "enumerations" (#5487)

[github-actions]

Commit: https://github.com/php/doc-en/commit/828980b619bb4300e196924598b6a5d398f630e4
PR: https://github.com/php/doc-en/pull/5487

Fichiers FR à mettre à jour

• language/types/singleton.xml