sysusers: many different errnos to express one condition

See https://bugzilla.redhat.com/show_bug.cgi?id=1807768. It turns
out that sysusers cannot query if the group exists:
Failed to check if group dnsmasq already exists: No such process
...
Failed to check if group systemd-timesync already exists: No such process

When the same command is executed later, the issue does not occur. Not sure why
the behaviour in the initial transaction is different. But let's accept all
errors that the man pages list. We check if the user/group exists before creating
anyway, so this seems pretty safe.

src/sysusers/sysusers.c

@@ -94,6 +94,12 @@ STATIC_DESTRUCTOR_REGISTER(database_groups, set_free_freep);
 STATIC_DESTRUCTOR_REGISTER(uid_range, freep);
 STATIC_DESTRUCTOR_REGISTER(arg_root, freep);
 
+static int errno_is_not_exists(int code) {
+        /* See getpwnam(3) and getgrnam(3): those codes and others can be returned if the user or group are
+         * not found. */
+        return IN_SET(code, 0, ENOENT, ESRCH, EBADF, EPERM);
+}
+
 static int load_user_database(void) {
         _cleanup_fclose_ FILE *f = NULL;
         const char *passwd_path;
@@ -971,7 +977,7 @@ static int add_user(Item *i) {
 
                         return 0;
                 }
-                if (!IN_SET(errno, 0, ENOENT))
+                if (!errno_is_not_exists(errno))
                         return log_error_errno(errno, "Failed to check if user %s already exists: %m", i->name);
         }
 
@@ -1108,7 +1114,7 @@ static int get_gid_by_name(const char *name, gid_t *gid) {
                         *gid = g->gr_gid;
                         return 0;
                 }
-                if (!IN_SET(errno, 0, ENOENT))
+                if (!errno_is_not_exists(errno))
                         return log_error_errno(errno, "Failed to check if group %s already exists: %m", name);
         }