Update opam.yml

Author: jmid

.github/workflows/opam.yml

@@ -24,7 +24,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Install OCaml compiler
         uses: ocaml/setup-ocaml@v2