ci: re-try OBS distrotests

Often, the VM fails to boot (even twice in the row, as already handled
by the test itself) which leads to false negative result.

These nightly tests fail far too often (at least on of the ~7 tests) and
generate annoying notifications.

Adding yet another layer of retries should reduce the number of false
negatives without diminishing the value of the test (since the real
packaging issues are 100 % reproducible).

.gitlab-ci.yml

@@ -516,6 +516,10 @@ obs:build:all:
     expire_in: 1 week
     paths:
       - ./j*
+  retry:
+    max: 1
+    when:
+      - script_failure
 
 obs:centos7:x86_64:
   <<: *distrotest