common.yaml: add dnf

As per discussions in
coreos/fedora-coreos-tracker#1687, we will add
dnf to RHCOS so it can be used for derivation.

common.yaml

@@ -169,8 +169,6 @@ check-groups:
 exclude-packages:
   # https://bugzilla.redhat.com/show_bug.cgi?id=1798278
   - subscription-manager
-  # And this one shouldn't come in
-  - dnf
   # https://github.com/coreos/rpm-ostree/pull/1789/files/a0cd999a8acd5b40ec1024a794a642916fbc8ff8#diff-fc2076dc46933204a7a798f544ce3734
   # People need to use `rpm-ostree kargs` instead.
   - grubby
@@ -246,6 +244,8 @@ packages:
  - crypto-policies-scripts
  # For semanage
  - policycoreutils-python-utils
+ # https://github.com/coreos/fedora-coreos-tracker/issues/1687
+ - dnf
 
 packages-x86_64:
   # Temporary add of open-vm-tools. Should be removed when containerized