R1:4e7c10cec54f

Fix a duplicate `case` statement

Summary: This appears to be a typo, identified by `ArcanistXHPASTLinter::LINT_DUPLICATE_SWITCH_CASE` (see D11171).

Test Plan: `arc lint`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11194