Allow partially migrated repositories to continue migration

Previously we verified if the projecthave at least migrated their
repository to hashed storage and prevented the migration command to
start a new migration.

The new version checks for the latest storage version available
(fully migrated), otherwise it allows migration to be triggered again.

app/models/project.rb

@@ -1968,7 +1968,7 @@ class Project < ActiveRecord::Base
   end
   def migrate_to_hashed_storage!
-    return if hashed_storage?(:repository)
+    return unless storage_upgradable?
     update!(repository_read_only: true)

changelogs/unreleased/53700-hashed-storagemigration.yml

+---
+title: 'Hashed Storage: allow migration to be retried in partially migrated projects'
+merge_request: 23087
+author:
+type: fixed

spec/models/project_spec.rb

@@ -3087,6 +3087,14 @@ describe Project do
       it 'does not flag as read-only' do
         expect { project.migrate_to_hashed_storage! }.not_to change { project.repository_read_only }
       end
+
+      context 'when partially migrated' do
+        it 'returns true' do
+          project = create(:project, storage_version: 1, skip_disk_validation: true)
+
+          expect(project.migrate_to_hashed_storage!).to be_truthy
+        end
+      end
     end
   end