Cache the commit author in RequestStore to avoid extra lookups in PostReceive

In a PostReceive task with 697 commits (8.9 RC1 -> RC8), looking up
the commit author takes about 10% of the time. Caching this information
in RequestStore saves a few seconds from the overall processing time.

Improves #18663

CHANGELOG

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.11.0 (unreleased)
   - Remove magic comments (`# encoding: UTF-8`) from Ruby files. !5456 (winniehell)
   - Fix CI status icon link underline (ClemMakesApps)
+  - Cache the commit author in RequestStore to avoid extra lookups in PostReceive
   - Fix of 'Commits being passed to custom hooks are already reachable when using the UI'
   - Add support for using RequestStore within Sidekiq tasks via SIDEKIQ_REQUEST_STORE env variable
   - Limit git rev-list output count to one in forced push check

app/models/commit.rb

@@ -178,7 +178,14 @@ class Commit
   end
 
   def author
-    @author ||= User.find_by_any_email(author_email.downcase)
+    key = "commit_author:#{author_email}"
+
+    # nil is a valid value since no author may exist in the system
+    unless RequestStore.store.has_key?(key)
+      RequestStore.store[key] = User.find_by_any_email(author_email.downcase)
+    end
+
+    @author ||= RequestStore.store[key]
   end
 
   def committer