bots: Fix broken apt sources on debian-stable
bots: Fix broken apt sources on debian-stable

The last line is not terminated with a newline, so the newly added line
for security updates both doesn't work and also breaks the
stable-updates apt source. It was also mis-formatted, the previous
"updates/main" ceased to work some time ago. Use the official syntax.

Fixes #8929
Closes #8944

cockpituous/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,mareklibra/cockpit,mareklibra/cockpit,cockpit-project/cockpit,andreasn/cockpit,stefwalter/cockpit,mareklibra/cockpit,stefwalter/cockpit,cockpit-project/cockpit,SotolitoLabs/cockpit,garrett/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,mvollmer/cockpit,mareklibra/cockpit,mvollmer/cockpit,SotolitoLabs/cockpit,andreasn/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,andreasn/cockpit,stefwalter/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,deryni/cockpit,andreasn/cockpit,mvollmer/cockpit,stefwalter/cockpit,deryni/cockpit,deryni/cockpit,cockpit-project/cockpit,cockpituous/cockpit,garrett/cockpit,SotolitoLabs/cockpit,cockpituous/cockpit,mareklibra/cockpit,mareklibra/cockpit,mareklibra/cockpit,martinpitt/cockpit,andreasn/cockpit,garrett/cockpit,moraleslazaro/cockpit,deryni/cockpit,andreasn/cockpit,stefwalter/cockpit,martinpitt/cockpit,garrett/cockpit,SotolitoLabs/cockpit,deryni/cockpit,deryni/cockpit,cockpituous/cockpit,garrett/cockpit,cockpituous/cockpit,deryni/cockpit,martinpitt/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit