talkback: post test suite results to MRs from forks again
This reverts commit 17be129b.
As we discussed in tails!1335 (comment 223782) it is useful to be able to push a contributor's branch (after reviewing that it is safe to run on jenkins) and then get the test suite results posted on their MR. The description of sysadmin#18062 (closed) also mentions that this should be safe now that we have "outdated commit" check.