qa/suites/rados/encoder: exclude ceph-osd-* when installing LTS releases

qa/suites/rados/encoder: exclude ceph-osd-* when installing LTS releases

In a37b5b5, the ceph-osd-classic and ceph-osd-crimson packages were
added to qa/packages/packages.yaml. The "install" task uses this file as
the default package list for all branches, including LTS releases like
Reef.

However, a37b5b5 only exists in the main branch and won't be backported
to LTS branches. This causes installation failures in the rados/encoder
test suite, which verifies forward compatibility by installing LTS
releases and testing whether they can decode the latest corpus.

Exclude ceph-osd-classic and ceph-osd-crimson from LTS installations to
ensure the test suite can successfully install ceph-dencoder, which is
required for the interoperability tests.

Fixes: https://tracker.ceph.com/issues/73957
Signed-off-by: Kefu Chai <k.chai@proxmox.com>