drop a FIXME on enabling/disabling repos with sed

dnf5 config-manager can now do this, but the syntax is different
to dnf4, and honestly, it seems easier to just stick with this
going forward than make it conditional on dnf version until
dnf4 goes away. So let's stop marking this as a FIXME.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

lib/utils.pm

@@ -496,7 +496,8 @@ sub disable_updates_repos {
         both => 0,
         @_
     );
-    # FIXME as of 2023-06-20 dnf5 doesn't have config-manager plugin yet :(
+    # we used to do this with config-manager, but the syntax differs
+    # on dnf 4 vs. dnf 5 and really sed is just as easy
     assert_script_run 'sed -i -e "s,enabled=1,enabled=0,g" /etc/yum.repos.d/fedora-updates-testing.repo';
     assert_script_run 'sed -i -e "s,enabled=1,enabled=0,g" /etc/yum.repos.d/fedora-updates.repo' if ($args{both});
     unless (script_run 'test -f /etc/yum.repos.d/fedora-updates-testing-modular.repo') {