Fix OlderDeploymentsDropService drops manual deployments

Currently, older manual jobs are dropped in the feature,
however, this is not an ideal from users.

This commit fixes the behavior by ignoring manual jobs.

Changelog: fixed

app/services/deployments/older_deployments_drop_service.rb

@@ -12,6 +12,8 @@ module Deployments
       return unless @deployment&.running?
 
       older_deployments_builds.each do |build|
+        next if build.manual?
+
         Gitlab::OptimisticLocking.retry_lock(build, name: 'older_deployments_drop') do |build|
           build.drop(:forward_deployment_failure)
         end

spec/services/deployments/older_deployments_drop_service_spec.rb

@@ -70,13 +70,12 @@ RSpec.describe Deployments::OlderDeploymentsDropService do
             let(:older_deployment) { create(:deployment, :created, environment: environment, deployable: build) }
             let(:build) { create(:ci_build, :manual) }
 
-            it 'drops the older deployment' do
-              deployable = older_deployment.deployable
-              expect(deployable.failed?).to be_falsey
+            # Manual jobs should not be accounted as outdated deployment jobs.
+            # See https://gitlab.com/gitlab-org/gitlab/-/issues/255978 for more information.
+            it 'does not drop any builds nor track the exception' do
+              expect(Gitlab::ErrorTracking).not_to receive(:track_exception)
 
-              subject
-
-              expect(deployable.reload.failed?).to be_truthy
+              expect { subject }.not_to change { Ci::Build.failed.count }
             end
           end