fix: Xen Version checks (#6708)

I missed a few cases...

Author: GabrielBuica

ocaml/tests/test_helpers.ml

@@ -507,6 +507,8 @@ module Version = struct
         , [25; 15; 0; 13]
         )
       ; ("Default version", "0.0.0", [0; 0; 0])
+      ; ("Xen Debug build version", "4.17.5-20-d", [4; 17; 5; 20])
+      ; ("Xen dev build version", "4.17.5-20.abcd", [4; 17; 5; 20])
       ]
     in
     let test_version_numbers (description, version_string, expected) =

ocaml/xapi/helpers.ml

@@ -937,9 +937,9 @@ module Checks = struct
 
   let version_numbers_of_string version_string =
     ( match String.split_on_char '-' version_string with
-    | [standard_version; patch] ->
-        String.split_on_char '.' standard_version @ [patch]
-    | [standard_version] ->
+    | standard_version :: patch :: _ ->
+        List.concat_map (String.split_on_char '.') [standard_version; patch]
+    | standard_version :: [] ->
         String.split_on_char '.' standard_version
     | _ ->
         ["0"; "0"; "0"]