Use Commit#author so we share logic and cache

Closes #24900

lib/gitlab/identifier.rb

@@ -21,10 +21,8 @@ module Gitlab
 
       return if !commit || !commit.author_email
 
-      email = commit.author_email
-
-      identify_with_cache(:email, email) do
-        User.find_by_any_email(email)
+      identify_with_cache(:email, commit.author_email) do
+        commit.author
       end
     end
 

spec/lib/gitlab/identifier_spec.rb

@@ -40,7 +40,7 @@ describe Gitlab::Identifier do
 
   describe '#identify_using_commit' do
     it "returns the User for an existing commit author's Email address" do
-      commit = double(:commit, author_email: user.email)
+      commit = double(:commit, author: user, author_email: user.email)
 
       expect(project).to receive(:commit).with('123').and_return(commit)
 
@@ -62,10 +62,9 @@ describe Gitlab::Identifier do
     end
 
     it 'caches the found users per Email' do
-      commit = double(:commit, author_email: user.email)
+      commit = double(:commit, author: user, author_email: user.email)
 
       expect(project).to receive(:commit).with('123').twice.and_return(commit)
-      expect(User).to receive(:find_by_any_email).once.and_call_original
 
       2.times do
         expect(identifier.identify_using_commit(project, '123')).to eq(user)