Fix using MySQL in recent AppVeyor environments

They don't have MySQL 5.7 any more but only 8.x and starting mysql
service doesn't work any longer, so it has to be done manually, see
appveyor/ci#3894

appveyor.yml

@@ -12,41 +12,46 @@ environment:
       BOOST_ROOT: C:\Libraries\boost_1_77_0
       MSSQL_VER: 2019
       POSTGRESQL_ROOT: C:\Program Files\PostgreSQL\13
-      MYSQL_DIR: C:\Program Files\MySql\MySQL Server 5.7
+      MYSQL_VER: 80
+      MYSQL_DIR: C:\Program Files\MySql\MySQL Server 8.0
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2022
     - G: "Visual Studio 16 2019"
       BOOST_ROOT: C:\Libraries\boost_1_73_0
       MSSQL_VER: 2017
       POSTGRESQL_ROOT: C:\Program Files\PostgreSQL\12
-      MYSQL_DIR: C:\Program Files\MySql\MySQL Server 5.7
+      MYSQL_VER: 80
+      MYSQL_DIR: C:\Program Files\MySql\MySQL Server 8.0
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
     - G: "Visual Studio 15 2017 Win64"
       BOOST_ROOT: C:\Libraries\boost_1_69_0
       MSSQL_VER: 2016
       POSTGRESQL_ROOT: C:\Program Files\PostgreSQL\11
+      MYSQL_VER: 57
       MYSQL_DIR: C:\Program Files\MySql\MySQL Server 5.7
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
     - G: "Visual Studio 14 2015 Win64"
       BOOST_ROOT: C:\Libraries\boost_1_60_0
       MSSQL_VER: 2014
       POSTGRESQL_ROOT: C:\Program Files\PostgreSQL\10
+      MYSQL_VER: 57
       MYSQL_DIR: C:\Program Files\MySql\MySQL Server 5.7
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
     - G: "MinGW Makefiles"
       MINGW_BIN: C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin
       MSSQL_VER: 2014
       BOOST_ROOT: C:\Libraries\boost_1_60_0
       POSTGRESQL_ROOT: C:\Program Files\PostgreSQL\9.4
+      MYSQL_VER: 57
       MYSQL_DIR: C:\Program Files\MySql\MySQL Server 5.7
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
 
 services:
-  - mysql
   - postgresql
 
 install:
-  # Start this one here as we can't specify the service name dynamically.
+  # Start these ones here as we can't specify the service name dynamically above.
   - net start mssql$SQL%MSSQL_VER%
+  - net start mysql%MYSQL_VER%
   - ps: |
       Import-Module C:\projects\soci\scripts\windows\Get-ODBCList.ps1
       $drivers_list = Get-ODBCList