AppVeyor: Restore MySQL (#1998)

Looks like the image was borked with MySQL 8 went in (because it's still trying to start 5.7), see appveyor/ci#3894.

appveyor.yml

@@ -19,7 +19,7 @@ environment:
   POSTGRES_ENV_POSTGRES_PASSWORD: Password12!
   POSTGRES_ENV_POSTGRES_DB: test
   # MySQL
-  MYSQL_PATH: C:\Program Files\MySql\MySQL Server 5.7
+  MYSQL_PATH: C:\Program Files\MySQL\MySQL Server 8.0
   MYSQL_PWD: Password12!
   MYSQL_ENV_MYSQL_USER: root
   MYSQL_ENV_MYSQL_PASSWORD: Password12!
@@ -38,15 +38,18 @@ init:
   - git config --global core.autocrlf input
   - SET PATH=%POSTGRES_PATH%\bin;%MYSQL_PATH%\bin;%PATH%
   - net start MSSQL$SQL2019
+  - ps: Start-Service MySQL80
 
 nuget:
   disable_publish_on_pr: true
 
-build_script:
+before_build:
   # Postgres
   - createdb test
   # MySQL
-  # - mysql -e "create database test;" --user=root
+  - '"C:\Program Files\MySQL\MySQL Server 8.0\bin\mysql" -e "create database test;" --user=root'
+
+build_script:
   # Our stuff
   - ps: .\build.ps1 -PullRequestNumber "$env:APPVEYOR_PULL_REQUEST_NUMBER" -CreatePackages $true