S-expressions test: Call gkm_crypto_sign_xsa with correct size type

The underlying type for gsize can be unsigned int, which is a distinct
type from unsigned long (the type behind CK_ULONG). The mismatch
results in compilation failures with GCC 14.

Submitted upstream: <https://gitlab.gnome.org/GNOME/gnome-keyring/-/merge_requests/63>

diff --git a/pkcs11/gkm/test-sexp.c b/pkcs11/gkm/test-sexp.c
index ba104a0e5b776669..fccf672353ddf42f 100644
--- a/pkcs11/gkm/test-sexp.c
+++ b/pkcs11/gkm/test-sexp.c
@@ -224,7 +224,7 @@ test_sign_verify (Test *test, gconstpointer unused)
 	guchar data[] = TEST_DATA;
 	guchar data_size = TEST_DATA_SIZE;
 	guchar signature[128];
-	gsize signature_size = 128;
+	CK_ULONG signature_size = 128;
 
 	/* RSA */
 	/* sign some data */