Fix breakage caused by LLVM commit:
commit 57109befac92811d2253109242ca6fa69c961fb2
Author: Aiden Grossman <aidengrossman@google.com>
Date: Sat Jun 13 08:35:21 2026 +0000
Reapply "[lit] Deprecate execute_external=True in ShTest" (#203316) (#203689)