Refactor DEFAULT_SCHEMA_MIGRATIONS_PATH

Use class_attribute instead,
to facilitate the modification of the default value.

lib/gitlab/database/schema_migrations/context.rb

@@ -6,7 +6,7 @@ module Gitlab
       class Context
         attr_reader :connection
 
-        DEFAULT_SCHEMA_MIGRATIONS_PATH = "db/schema_migrations"
+        class_attribute :default_schema_migrations_path, default: 'db/schema_migrations'
 
         def initialize(connection)
           @connection = connection
@@ -30,7 +30,7 @@ module Gitlab
         end
 
         def database_schema_migrations_path
-          @connection.pool.db_config.configuration_hash[:schema_migrations_path] || DEFAULT_SCHEMA_MIGRATIONS_PATH
+          @connection.pool.db_config.configuration_hash[:schema_migrations_path] || self.class.default_schema_migrations_path
         end
       end
     end

spec/lib/gitlab/database/schema_migrations/context_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe Gitlab::Database::SchemaMigrations::Context do
 
   describe '#schema_directory' do
     it 'returns db/schema_migrations' do
-      expect(context.schema_directory).to eq(File.join(Rails.root, 'db/schema_migrations'))
+      expect(context.schema_directory).to eq(File.join(Rails.root, described_class.default_schema_migrations_path))
     end
 
     context 'CI database' do
@@ -19,7 +19,7 @@ RSpec.describe Gitlab::Database::SchemaMigrations::Context do
       it 'returns a directory path that is database specific' do
         skip_if_multiple_databases_not_setup
 
-        expect(context.schema_directory).to eq(File.join(Rails.root, 'db/schema_migrations'))
+        expect(context.schema_directory).to eq(File.join(Rails.root, described_class.default_schema_migrations_path))
       end
     end