fix: resolve enable_introspection env variable at runtime (#1211) - #1247

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PHPDoc type array{name?: string|null, description?: string|null, serialize: callable(mixed): mixed, parseValue?: callable(mixed): mixed, parseLiteral?: callable(GraphQL\Language\AST\Node, array|null): mixed, astNode?: GraphQL\Language\AST\ScalarTypeDefinitionNode|null, extensionASTNodes?: array<GraphQL\Language\AST\ScalarTypeExtensionNode>|null, scalarType?: (callable(): GraphQL\Type\Definition\ScalarType)|GraphQL\Type\Definition\ScalarType|null} of property Overblog\GraphQLBundle\Definition\Type\CustomScalarType::$config is not covariant with PHPDoc type array{name?: string|null, description?: string|null, serialize?: callable(mixed): mixed, parseValue?: callable(mixed): mixed, parseLiteral?: callable(GraphQL\Language\AST\Node&GraphQL\Language\AST\ValueNode, array<string, mixed>|null): mixed, specifiedByURL?: string|null, astNode?: GraphQL\Language\AST\ScalarTypeDefinitionNode|null, extensionASTNodes?: array<GraphQL\Language\AST\ScalarTypeExtensionNode>|null}&non-empty-array of overridden property GraphQL\Type\Definition\CustomScalarType::$config.