repo: Stop using deprecated G_GNUC_FUNCTION

In glib 2.62 this has been changed to emitting a warning. Use G_STRFUNC
instead, which has been available for a long time and is already used in
other places in ostree.

src/libostree/ostree-repo.c

@@ -1548,8 +1548,8 @@ keyfile_set_from_vardict (GKeyFile     *keyfile,
           g_key_file_set_string_list (keyfile, section, key, strv_child, len);
         }
       else
-        g_critical ("Unhandled type '%s' in " G_GNUC_FUNCTION,
-                    (char*)g_variant_get_type (child));
+        g_critical ("Unhandled type '%s' in %s",
+                    (char*)g_variant_get_type (child), G_STRFUNC);
     }
 }