minor #16515 [Doctrine] Recommend a better charset for MySQL (greg0ire)

This PR was merged into the 5.4 branch. Discussion ---------- [Doctrine] Recommend a better charset for MySQL UTF8 is meant to be used when using PostgreSQL, and the example is mainly about MySQL. In the case of MySQL, utf8 is a deprecated charset and should not be used. <!-- If your pull request fixes a BUG, use the oldest maintained branch that contains the bug (see https://symfony.com/releases for the list of maintained branches). If your pull request documents a NEW FEATURE, use the same Symfony branch where the feature was introduced (and `6.x` for features of unreleased versions). --> Commits ------- 4f5845b Recommend a better charset for MySQL

Author: javiereguiluz

reference/configuration/doctrine.rst

@@ -62,7 +62,7 @@ The following block shows all possible configuration keys:
  unix_socket: /tmp/mysql.sock
  # the DBAL wrapperClass option
  wrapper_class: App\DBAL\MyConnectionWrapper
- charset: UTF8
+ charset: utf8mb4
  logging: '%kernel.debug%'
  platform_service: App\DBAL\MyDatabasePlatformService
  server_version: '5.7'
@@ -96,7 +96,7 @@ The following block shows all possible configuration keys:
  memory="true"
  unix-socket="/tmp/mysql.sock"
  wrapper-class="App\DBAL\MyConnectionWrapper"
- charset="UTF8"
+ charset="utf8mb4"
  logging="%kernel.debug%"
  platform-service="App\DBAL\MyDatabasePlatformService"
  server-version="5.7">