Issue #3618284: TEMPORARY - point at entity_sync D11 fork for CI

Same as the temporary override used in #3450001 - the real entity_sync release doesn't support D11 yet, so the D11 CI job needs this to install successfully and actually run phpcs/phpstan. Must be reverted before merging, once entity_sync's own MR (#3459602) lands upstream and a real D11-compatible release exists.

Closes #3618284