Make AbstractSchemaManager covariant to its template argument

[zerkms]

Q	A
Type	bug
Fixed issues

Summary

<?php
declare(strict_types=1);

abstract class AbstractPlatform {}

class PostgreSQLPlatform extends AbstractPlatform {}

/**
 * @template T of AbstractPlatform
 */
abstract class AbstractSchemaManager {}

/**
 * @extends AbstractSchemaManager<PostgreSQLPlatform>
 */
class PostgreSQLSchemaManager extends AbstractSchemaManager {}

function createSchemaManager(): AbstractSchemaManager
{
    return new PostgreSQLSchemaManager();
}

$schemaManager = createSchemaManager();

if (!$schemaManager instanceof PostgreSQLSchemaManager) {}

ERROR: [RedundantCondition](https://psalm.dev/122) - 25:6 - AbstractSchemaManager<AbstractPlatform> cannot be identical to PostgreSQLSchemaManager

vs

<?php
declare(strict_types=1);

abstract class AbstractPlatform {}

class PostgreSQLPlatform extends AbstractPlatform {}

/**
 * @template-covariant T of AbstractPlatform
 */
abstract class AbstractSchemaManager {}

/**
 * @extends AbstractSchemaManager<PostgreSQLPlatform>
 */
class PostgreSQLSchemaManager extends AbstractSchemaManager {}

function createSchemaManager(): AbstractSchemaManager
{
    return new PostgreSQLSchemaManager();
}

$schemaManager = createSchemaManager();

if (!$schemaManager instanceof PostgreSQLSchemaManager) {}

No issues!