Always require verification of backend and frontend changes on merge commits

I2db698b9 is an example where neither the Verified SR, not the
Frontend-Verified was required. The change is a clean merge of a
stable branch into master.

The conditions are based on the file predicate which is operating on
an empty list of files for clean merges. To make the SRs applicable,
we make them explicitly applicable on merge commits.

Google-Bug: b/312738713
Change-Id: I13f63462d150a93b014f9b836596c3464d2bd56f
1 file changed
tree: d842329d6c2c2d8a206d3436eda0c2dcd992aec9
  1. buildbucket.config
  2. groups
  3. project.config
  4. tricium.config