Handle case where deployment ref no longer exists

Keep-around refs for deployments were only introduced in 8.10, so any
deployment created in 8.9 could have a SHA pointing to a commit that no
longer exists in the repository. We can't do anything useful with those
deployments, so make `#includes_commit?` always return false for those.

app/models/deployment.rb

@@ -40,7 +40,14 @@ class Deployment < ActiveRecord::Base
   def includes_commit?(commit)
     return false unless commit
 
+    # Before 8.10, deployments didn't have keep-around refs. Any deployment
+    # created before then could have a `sha` referring to a commit that no
+    # longer exists in the repository, so just ignore those.
+    begin
       project.repository.is_ancestor?(commit.id, sha)
+    rescue Rugged::OdbError
+      false
+    end
   end
 
   def update_merge_request_metrics!

spec/models/deployment_spec.rb

@@ -38,5 +38,14 @@ describe Deployment, models: true do
         expect(deployment.includes_commit?(commit)).to be true
       end
     end
+
+    context 'when the SHA for the deployment does not exist in the repo' do
+      it 'returns false' do
+        deployment.update(sha: Gitlab::Git::BLANK_SHA)
+        commit = project.commit
+
+        expect(deployment.includes_commit?(commit)).to be false
+      end
+    end
   end
 end