Release v2.9.3

[![Build Status](https://travis-ci.org/doctrine/dbal.svg?branch=v2.9.3)](https://travis-ci.org/doctrine/dbal)

This release fixes regressions introduced in previous releases and other bugs.

- Total issues resolved: **5**
- Total pull requests resolved: **14**
- Total contributors: **9**

**Regressions**

 - [3686: Fixed query result caching when `FetchMode::COLUMN` is used](https://github.com/doctrine/dbal/pull/3686) thanks to @morozov and @Junker

 - [3456: Compare type class when comparing columns.](https://github.com/doctrine/dbal/pull/3456) thanks to @garret-gunter and @cs278

**Other bugs**

 - [3679: fix begin trasaction after reconnect](https://github.com/doctrine/dbal/pull/3679) thanks to @kalinin-k-a

 - [3547: Default column expressions do not work on SQL Server](https://github.com/doctrine/dbal/pull/3547) thanks to @morozov

 - [3420: Index length can be a `string`: ensure that it is an integer when read by the `MySqlSchemaManager`](https://github.com/doctrine/dbal/pull/3420) thanks to @leofeyer

**CI improvements and maintenance**

 - [3702: Updated SQL Server extensions to fix build failures on PHP 7.4](https://github.com/doctrine/dbal/pull/3702) thanks to @morozov

 - [3662: Marked connection exception test incomplete on MySQL 8](https://github.com/doctrine/dbal/pull/3662) thanks to @morozov

 - [3622: Switched from ibmcom/db2express-c to ibmcom/db2](https://github.com/doctrine/dbal/pull/3622) thanks to @morozov

 - [3465: Replaced MySQL 5.7 installed from a PPA with an official Docker image](https://github.com/doctrine/dbal/pull/3465) thanks to @morozov

 - [3454: CI: Test against PHP 7.4snapshot instead of nightly (8.0)](https://github.com/doctrine/dbal/pull/3454) thanks to @Majkl578

 - [3452: Fixed AppVeyor build configuration and the issue on SQL Server](https://github.com/doctrine/dbal/pull/3452) thanks to @morozov and @Majkl578

 - [3447: Replaced custom docker image for PostgreSQL with the official one](https://github.com/doctrine/dbal/pull/3447) thanks to @morozov

 - [3407: CI: Test against MySQL 8.0 on Travis](https://github.com/doctrine/dbal/pull/3407) thanks to @morozov

**PHP 7.4 support**

 - [3642: Fixed test failures on PHP 7.4](https://github.com/doctrine/dbal/pull/3642) thanks to @morozov