Restore APT pinning of deb.tp.o

Originally created by @anonym on #13416 (Redmine)

I.e. revert commit 0e8ef1fe71bae0f48e8e65186a656e1e8169e7bc.

Feature Branch: bugfix/13416-restore-deb.tpo-APT-pinning

Edited May 15, 2020 by anonym

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