(mysql) Fix automatic MySQL update in `update.ps1`

[lauxjpn]

Description

• Changes the defunct download URL to the currently used one.
• Uses the GitHub tags page to get the latest release version number, instead of the download page of the MySQL site (an alternative would be to parse https://api.github.com/repos/mysql/mysql-server/tags instead).
• Specifies the mainline version prefix, since there can be multiple maintained release lines by Oracle.

Motivation and Context

• The currently used download URL is incorrect, because it was changed on the MySQL website.
• It is currently not possible to get the latest version, because the MySQL website requires a JavaScript enabled browser.

How Has this Been Tested?

I ran the update script locally:

PS C:\Repositories\chocolatey-packages\automatic\mysql> .\update.ps1
mysql - checking updates using au version 2022.10.24

URL check
  https://cdn.mysql.com/Downloads/MySQL-8.0/mysql-8.0.34-winx64.zip
nuspec version: 8.0.31
remote version: 8.0.34
New version is available
Automatic checksum started
Adding 'C:\tools\mysql\current\bin' to the path and the current shell path
PATH environment variable does not have C:\tools\mysql\current\bin in it. Adding...
Using system proxy server ''.
Downloading chocolatey\mysql 64 bit
  from 'https://cdn.mysql.com/Downloads/MySQL-8.0/mysql-8.0.34-winx64.zip'
Using system proxy server ''.

Download of mysql-8.0.34-winx64.zip (231,68 MB) completed.
Package downloaded and hash calculated for 64 bit version
Setting package description from README.md
Updating files
  $Latest data:
    Checksum64                (String)     d0480039bceef97a558027bfb868b77be1717ec1097410c697db383315243895
    ChecksumType64            (String)     sha256
    FileType                  (String)     zip
    NuspecVersion             (String)     8.0.31
    PackageName               (String)     mysql
    URL64                     (String)     https://cdn.mysql.com/Downloads/MySQL-8.0/mysql-8.0.34-winx64.zip
    Version                   (String)     8.0.34
  mysql.nuspec
    setting id: mysql
    updating version: 8.0.31 -> 8.0.34
  tools\chocolateyInstall.ps1
    (^[$]checksumType\s*=\s*)('.*')     = $1'sha256'
    (^[$]url\s*=\s*)('.*')              = $1'https://cdn.mysql.com/Downloads/MySQL-8.0/mysql-8.0.34-winx64.zip'
    (^[$]checksum\s*=\s*)('.*')         = $1'd0480039bceef97a558027bfb868b77be1717ec1097410c697db383315243895'
Attempting to build package from 'mysql.nuspec'.
Successfully created package 'C:\Repositories\chocolatey-packages\automatic\mysql\mysql.8.0.34.nupkg'

Package updated

Path          : C:\Repositories\chocolatey-packages\automatic\mysql
Name          : mysql
Updated       : True
Pushed        : False
RemoteVersion : 8.0.34
NuspecVersion : 8.0.31
Result        : {mysql - checking updates using au version 2022.10.24, , URL check,   https://cdn.mysql.com/Downloads/MySQL-8.0/mysql-8.0.34-winx64.zip…}
Error         :
NuspecPath    : C:\Repositories\chocolatey-packages\automatic\mysql\mysql.nuspec
NuspecXml     : #document
Ignored       : False
IgnoreMessage :
StreamsPath   : C:\Repositories\chocolatey-packages\automatic\mysql\mysql.json
Streams       :

Screenshot (if appropriate, usually isn't needed):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Migrated package (a package has been migrated from another repository)

Checklist:

• [x] My code follows the code style of this repository.
• [ ] My change requires a change to documentation (this usually means the notes in the description of a package).
• [ ] I have updated the documentation accordingly (this usually means the notes in the description of a package).
• [ ] I have updated the package description and it is less than 4000 characters.
• [x] All files are up to date with the latest Contributing Guidelines
• [ ] The added/modified package passed install/uninstall in the chocolatey test environment.
• [x] The changes only affect a single package (not including meta package).

[AppVeyorBot]

:white_check_mark: Package verification completed without issues. PR is now pending human review