Merge branch 'dont-touch-fs-on-pipeline-save' into 'master'

Keep around commits only on pipeline create

## What does this MR do?
Since the pipeline SHA doesn't change, we don't need to update keep arounds every save.

## Why was this MR needed?
This is minimal change to fix this: https://gitlab.com/gitlab-org/gitlab-ce/issues/23503

See merge request !6986

CHANGELOG.md

@@ -16,6 +16,7 @@ Please view this file on the master branch, on stable branches it's out of date.
   - Ability to resolve merge request conflicts with editor !6374
   - Add `/projects/visible` API endpoint (Ben Boeckel)
   - Fix centering of custom header logos (Ashley Dumaine)
+  - Keep around commits only pipeline creation as pipeline data doesn't change over time
   - ExpireBuildArtifactsWorker query builds table without ordering enqueuing one job per build to cleanup
   - Add an example for testing a phoenix application with Gitlab CI in the docs (Manthan Mallikarjun)
   - Cancelled pipelines could be retried. !6927

app/models/ci/pipeline.rb

@@ -19,7 +19,7 @@ module Ci
     validates_presence_of :status, unless: :importing?
     validate :valid_commit_sha, unless: :importing?
 
-    after_save :keep_around_commits, unless: :importing?
+    after_create :keep_around_commits, unless: :importing?
 
     delegate :stages, to: :statuses