Fix test for OCaml 5

The format of the error that this test checks for is printed a little
differently by the OCaml 5 compiler (the name of the tag is now quoted).
Adapt the test a little to make it work both for OCaml 4 and 5.

Signed-off-by: Rob Hoes <[email protected]>

Author: robhoes

ocaml/libs/xapi-stdext/lib/xapi-fdcaps/test/properties.t

@@ -4,12 +4,14 @@ Check that we get compile errors when trying to use a read-only or write-only pr
   > open Xapi_fdcaps.Properties
   > let _ = as_readable (make `wronly `reg)
   > EOF
-  $ ocamlfind ocamlc -package xapi-stdext-unix.fdcaps -c t.ml 2>&1 | tail -n 1
-         The second variant type does not allow tag(s) `wronly
+  $ ocamlfind ocamlc -package xapi-stdext-unix.fdcaps -c t.ml 2>&1 |
+  > grep -c "The second variant type does not allow tag(s)"
+  1
 
   $ cat >t.ml <<'EOF'
   > open Xapi_fdcaps.Properties
   > let _ = as_writable (make `rdonly `reg)
   > EOF
-  $ ocamlfind ocamlc -package xapi-stdext-unix.fdcaps -c t.ml 2>&1 | tail -n 1
-         The second variant type does not allow tag(s) `rdonly
+  $ ocamlfind ocamlc -package xapi-stdext-unix.fdcaps -c t.ml 2>&1 |
+  > grep -c "The second variant type does not allow tag(s)"
+  1