effects keyword can be an attribute id (#2714)

Author: EmileTrotignon

test/passing/refs.ahrefs/attributes.ml.ref

@@ -584,3 +584,5 @@ let _ =
 
 let fold input ~init ~f =
   foldi input ~init ~f:(fun (_ : int) acc x -> f acc x) [@nontail]
+
+[@@@effect]

test/passing/refs.default/attributes.ml.ref

@@ -463,3 +463,5 @@ let _ =
 
 let fold input ~init ~f =
   foldi input ~init ~f:(fun (_ : int) acc x -> f acc x) [@nontail]
+
+[@@@effect]

test/passing/refs.janestreet/attributes.ml.ref

@@ -535,3 +535,5 @@ let _ =
 ;;
 
 let fold input ~init ~f = foldi input ~init ~f:(fun (_ : int) acc x -> f acc x) [@nontail]
+
+[@@@effect]

test/passing/refs.ocamlformat/attributes.ml.ref

@@ -513,3 +513,5 @@ let _ =
 
 let fold input ~init ~f =
   foldi input ~init ~f:(fun (_ : int) acc x -> f acc x) [@nontail]
+
+[@@@effect]

test/passing/tests/attributes.ml

@@ -498,3 +498,5 @@ let _ = (begin[@a] x end [@b])
 
 let fold input ~init ~f =
   foldi input ~init ~f:(fun (_ : int) acc x -> f acc x) [@nontail]
+
+[@@@effect]