More space between multiple errors, no numbers if just one

compiler/catala_utils/message.ml

@@ -326,10 +326,14 @@ module Content = struct
         ppf content;
       Format.pp_print_newline ppf ()
 
-  let emit_n (target : level) (contents : t list) : unit =
+  let emit_n (target : level) = function
+    | [content] -> emit content target
+    | contents ->
+      let ppf = get_ppf target in
       let len = List.length contents in
       List.iteri
         (fun i c ->
+          if i > 0 then Format.pp_print_newline ppf ();
           let extra_label = Printf.sprintf "(%d/%d)" (succ i) len in
           let pp_marker ?extra_label:_ = pp_marker ~extra_label in
           emit ~pp_marker c target)

tests/bool/bad/test_xor_with_int.catala_en

@@ -29,6 +29,7 @@ $ catala Typecheck
 │ 8 │   definition test_var equals 10 xor 20
 │   │                                 ‾‾‾
 └─ 'xor' should be a boolean operator
+
 ┌─[ERROR (2/2)]─
 │
 │  Error during typechecking, incompatible types:

tests/parsing/bad/multiple_errors.catala_en

@@ -32,6 +32,7 @@ $ catala test-scope A
 │
 │ Maybe you wanted to write : "definition" ?
 └─
+
 ┌─[ERROR (2/2)]─
 │
 │  Syntax error at "equal":

tests/typing/bad/mult_errs1.catala_en

@@ -30,6 +30,7 @@ $ catala Typecheck
 │ 8 │   data i content integer
 │   │                  ‾‾‾‾‾‾‾
 └─
+
 ┌─[ERROR (2/2)]─
 │
 │  Error during typechecking, incompatible types: