Revert temporary changes to pr-ci-testing

This reverts the following commits:
a838080 Add PR-850-merge to the temporary exceptions
8c51a48 Temporarily enable automatic runs of PR-906-merge

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
Change-Id: Id0a08c4ca5842774b82cc499839a9833693e6f4f
1 file changed