[tests] Explicitly pass --yes for ounit install step (#9243)

Summary:
CI jobs starts to fail because of lack of --yes recently.

Pull Request resolved: #9243

Reviewed By: SamChou19815

Differential Revision: D67802088

fbshipit-source-id: 9ccc83cac859b4733d225ab604dc16e62cd47303

Makefile

@@ -59,7 +59,7 @@ deps-js:
 
 .PHONY: deps-test
 deps-test:
-	opam install ounit$(OUNIT_VERSION)
+	opam install ounit$(OUNIT_VERSION) --yes
 
 clean:
 	if command -v dune >/dev/null; then dune clean; fi