nspawn: use ERRNO_IS_NEG_NOT_SUPPORTED() at one more place

Follow-up for dc3223919f.
Addresses https://github.com/systemd/systemd/pull/34067#discussion_r1748061156.

Error codes other than ENOSYS may not come here, but if it comes, still
there is nothing we can do here, so let's not log the failure loudly.

src/nspawn/nspawn.c

@@ -2208,7 +2208,7 @@ static bool should_enable_fuse(void) {
         if (r < 0) {
                 if (ERRNO_IS_NEG_DEVICE_ABSENT(r))
                         log_debug_errno(r, "Disabling FUSE: FUSE appears to be disabled on the host: %m");
-                else if (r == -ENOSYS)
+                else if (ERRNO_IS_NEG_NOT_SUPPORTED(r))
                         log_debug_errno(r, "Disabling FUSE: Kernel does not support the fsopen() family of syscalls: %m");
                 else
                         log_warning_errno(r, "Disabling FUSE: Failed to determine FUSE version: %m");