Bump OCaml 5 to alpha1 in CI

Author: sim642

.github/workflows/tests.yml

@@ -25,7 +25,7 @@ jobs:
           - 4.12.0
           - 4.13.1
           - 4.14.x
-          - ocaml-base-compiler.5.0.0~alpha0
+          - ocaml-base-compiler.5.0.0~alpha1
 
 
     runs-on: ${{ matrix.os }}