test-resolved: fix error code check in assertion

If file "/etc/hosts" does not exist, fopen fails and sets errno to ENOENT
("No such file or directory"). So errno should be compared with ENOENT.

This mistake causes test test-resolved-etc-hosts to fail when run on Debian
image built with mkosi.debian included in the repo. The image does not include
"/etc/hosts" file as it is not created by debootstrap, see debootstrap manpage
https://manpages.debian.org/stretch/debootstrap/debootstrap.8.en.html.

src/resolve/test-resolved-etc-hosts.c

@@ -11,7 +11,7 @@ static void test_parse_etc_hosts_system(void) {
 
         f = fopen("/etc/hosts", "re");
         if (!f) {
-                assert_se(errno == -ENOENT);
+                assert_se(errno == ENOENT);
                 return;
         }