Revert changes to config/database.yml.postgresql

This is temporary change to ensure
that application works properly
till we start using `main:` everywhere

config/database.yml.postgresql

@@ -2,7 +2,6 @@
 # PRODUCTION
 #
 production:
-  main:
   adapter: postgresql
   encoding: unicode
   database: gitlabhq_production
@@ -23,7 +22,6 @@ production:
 # Development specific
 #
 development:
-  main:
   adapter: postgresql
   encoding: unicode
   database: gitlabhq_development
@@ -37,7 +35,6 @@ development:
 # Staging specific
 #
 staging:
-  main:
   adapter: postgresql
   encoding: unicode
   database: gitlabhq_staging
@@ -49,7 +46,6 @@ staging:
 # re-generated from your development database when you run "rake".
 # Do not set this db to the same as development or production.
 test: &test
-  main:
   adapter: postgresql
   encoding: unicode
   database: gitlabhq_test

lib/gitlab/database.rb

@@ -76,7 +76,11 @@ module Gitlab
       # The database is `main` if it is a first entry in `database.yml`
       # Rails internally names them `primary` to avoid confusion
       # with broad `primary` usage we use `main` instead
-      ActiveRecord::Base.configurations.primary?(name.to_s)
+      #
+      # TODO: The explicit `== 'main'` is needed in a transition period till
+      # the `database.yml` is not migrated into `main:` syntax
+      # https://gitlab.com/gitlab-org/gitlab/-/merge_requests/65243
+      ActiveRecord::Base.configurations.primary?(name.to_s) || name.to_s == 'main'
     end
 
     def self.ci_database?(name)

spec/lib/gitlab/database/postgresql_adapter/type_map_cache_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Database::PostgresqlAdapter::TypeMapCache do
-  let(:db_config) { ActiveRecord::Base.configurations.configs_for(env_name: 'test', name: 'main').configuration_hash }
+  let(:db_config) { ActiveRecord::Base.configurations.find_db_config(env_name: 'test').configuration_hash }
   let(:adapter_class) { ActiveRecord::ConnectionAdapters::PostgreSQLAdapter }
 
   before do