Merge branch 'knapsack-update-results-only-on-master' into 'master'

Update Knapsack report only on master

## What does this MR do?

Makes to generate Knapsack report only on master. This speed-ups tests, because the last stage can be run significant time after previous stages.


See merge request !4540

.gitlab-ci.yml

@@ -61,6 +61,8 @@ update-knapsack:
     - scripts/merge-reports knapsack/rspec_report.json knapsack/rspec_node_*.json
     - scripts/merge-reports knapsack/spinach_report.json knapsack/spinach_node_*.json
     - rm -f knapsack/*_node_*.json
+  only:
+    - master
 
 # Execute all testing suites