TMT: include podman checkpoint system tests

`podman checkpoint...` tests depend on crun as well so they should be
included in the TMT system test runs. These are currently failing on
podman upstream PRs, for example: [0], [1] and [2].

[0]: https://artifacts.dev.testing-farm.io/fd5c08eb-2b0d-4ea8-9c33-ac9bf3447bd8/
[1]: https://artifacts.dev.testing-farm.io/e227ef00-c5c4-43e6-9785-0b5b5fcd2908/
[2]: https://artifacts.dev.testing-farm.io/c4ef6e7a-3b5d-4afc-91b9-dd477ef699e3/

Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org>

Author: lsm5

tests/tmt/podman/system-test.sh

@@ -14,3 +14,4 @@ rpm -q conmon containers-common crun podman podman-tests
 bats -t /usr/share/podman/test/system/030-run.bats
 bats -t /usr/share/podman/test/system/075-exec.bats
 bats -t /usr/share/podman/test/system/280-update.bats
+bats -t /usr/share/podman/test/system/520-checkpoint.bats