Motivation / Problem

Setup time for MSYS2 is quite slow (~90s) because we don't use the default installation, meaning MSYS2 is downloaded and installed every time.
And we also set the action to update the installation, using more time.
Then our packages are installed.

Description

With this change, it's more like for vcpkg, we just use the installation available in the virtual environment without updating it, and install our packages.
Setup time is reduced by ~60s.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker