Increase the memory limits used in the unicorn killer

These limits were updated in our docs, and in omnibus some time ago. But
the defaults in the source-install were missed.

changelogs/unreleased/increase-unicorn-memory-killer-limits.yml

+---
+title: Increase the memory limits used in the unicorn killer
+merge_request: 17948
+author:
+type: other

config.ru

@@ -7,8 +7,8 @@ if defined?(Unicorn)
     # Unicorn self-process killer
     require 'unicorn/worker_killer'
 
-    min = (ENV['GITLAB_UNICORN_MEMORY_MIN'] || 300 * 1 << 20).to_i
-    max = (ENV['GITLAB_UNICORN_MEMORY_MAX'] || 350 * 1 << 20).to_i
+    min = (ENV['GITLAB_UNICORN_MEMORY_MIN'] || 400 * 1 << 20).to_i
+    max = (ENV['GITLAB_UNICORN_MEMORY_MAX'] || 650 * 1 << 20).to_i
 
     # Max memory size (RSS) per worker
     use Unicorn::WorkerKiller::Oom, min, max