Free open file descriptors and libgit2 buffers in UpdatePagesService

In UpdatePagesService, we were seeing a large number of open pack files in
production. Calling Project#cleanup removes a reference to Rugged::Repository
and forces libgit2 to close file descriptors and free its internal memory
cache.

Relates to https://gitlab.com/gitlab-com/infrastructure/issues/3965#note_65837525

app/services/projects/update_pages_service.rb

@@ -178,6 +178,9 @@ module Projects
 
     def latest_sha
       project.commit(build.ref).try(:sha).to_s
+    ensure
+      # Close any file descriptors that were opened and free libgit2 buffers
+      project.cleanup
     end
 
     def sha

changelogs/unreleased/sh-cleanup-pages-worker.yml

+---
+title: Free open file descriptors and libgit2 buffers in UpdatePagesService
+merge_request:
+author:
+type: performance