Codechange: [CI] manually install vcpkg for all targets

[TrueBrain]

Motivation / Problem

From macos-14, vcpkg is no longer installed on the runner-image. It stands to reason that this will also roll out to new images for other OSes. To be pre-emptive about it, start using our own cloned vcpkg for all targets.

It is better to have all targets work the same, than some exceptions here, some exceptions there. Lowers the maintenance burden on our end.

Description

Use our own vcpkg for all targets.

PS: release-linux already did use its own vcpkg.

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 touches english.txt or translations? Check the guidelines
• 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, game_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

[TrueBrain]

Build release results:
https://github.com/TrueBrain/OpenTTD/actions/runs/8214264751/job/22466567424

This shows that the non-system vcpkg is now being used by all targets :)

[rubidium42]

Looks okay to me