Merge pull request #895 from Shrews/backport/890/release_2.1

[release_2.1] Switch project to squash-merge mode

Backport of PR #890
(cherry picked from commit 4e26023)

Reviewed-by: Sam Doran <[email protected]>
Reviewed-by: None <None>

Author: ansible-zuul[bot]

.zuul.d/project.yaml

@@ -1,5 +1,6 @@
 ---
 - project:
+    merge-mode: squash-merge
     check:
       jobs: &id001
         - ansible-buildset-registry