Fix db object to not return deprecated variable

Calling `db_config.config` was deprecated in rails#37185 in favor of
`db_config.configuration_hash`. When returning the objects from
`configurations` we should ensure the object returns the non-deprecated
method.

Before:

```
<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007ff0f61696a0
@env_name="development", @name="primary", @config={:adapter=>"mysql2",
:database=>"recipes_development"}>
```

After:

```
<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007ff0f61696a0
@env_name="development", @name="primary", @configuration_hash={:adapter=>"mysql2",
:database=>"recipes_development"}>
```

Co-authored-by: John Crepezzi <john.crepezzi@gmail.com>

activerecord/lib/active_record/database_configurations/hash_config.rb

@@ -25,20 +25,17 @@ class DatabaseConfigurations
     #   database adapter, name, and other important information for database
     #   connections.
     class HashConfig < DatabaseConfig
-      def initialize(env_name, name, config)
+      attr_reader :configuration_hash
+      def initialize(env_name, name, configuration_hash)
         super(env_name, name)
-        @config = config.symbolize_keys
+        @configuration_hash = configuration_hash.symbolize_keys.freeze
       end
 
       def config
         ActiveSupport::Deprecation.warn("DatabaseConfig#config will be removed in 6.2.0 in favor of DatabaseConfigurations#configuration_hash which returns a hash with symbol keys")
         configuration_hash.stringify_keys
       end
 
-      def configuration_hash
-        @config.freeze
-      end
-
       # Determines whether a database configuration is for a replica / readonly
       # connection. If the +replica+ key is present in the config, +replica?+ will
       # return +true+.
@@ -62,7 +59,7 @@ def database
       end
 
       def _database=(database) # :nodoc:
-        @config = configuration_hash.dup.merge(database: database).freeze
+        @configuration_hash = configuration_hash.merge(database: database).freeze
       end
 
       def pool

activerecord/lib/active_record/database_configurations/url_config.rb

@@ -31,11 +31,11 @@ class DatabaseConfigurations
     class UrlConfig < HashConfig
       attr_reader :url
 
-      def initialize(env_name, name, url, config = {})
-        super(env_name, name, config)
+      def initialize(env_name, name, url, configuration_hash = {})
+        super(env_name, name, configuration_hash)
 
         @url = url
-        @config.merge!(build_url_hash)
+        @configuration_hash = @configuration_hash.merge(build_url_hash).freeze
       end
 
       private