Fix CQS signal facebook-unused-include-check in fbcode/glean/rocksdb/tests

Reviewed By: pepeiborra

Differential Revision: D77583408

fbshipit-source-id: 8953ca29863e620b55e5477aae266c0d16edd15b

Author: Alena Chernikava

glean/rocksdb/tests/ffi_works_as_c.c

@@ -7,8 +7,7 @@
  */
 
 /* This file only exists to make sure that ffi.h can be included in a C file. */
-
-#include "glean/rocksdb/ffi.h"
+#include "glean/rocksdb/ffi.h" // IWYU pragma: keep
 
 int main() {
   return 0;