Fix MSYS hanging of PowerShell

[emptyVoid]

Fixes #6688.

I moved gpg-agent.exe termination code from #6407 into vcpkg_acquire_msys so that none of the ports using MSYS would block build automation tools.

[NancyLi1013]

Hi @emptyVoid, thanks for your PR. Could you please also bump the version in CONTROL version?

[emptyVoid]

@NancyLi1013, do you mean ports/icu/CONTROL file?

[NancyLi1013]

Yes, you're right. if there are some changes about the port, you should also update the version in ports/port/CONTROL file. Thanks.

[emptyVoid]

Same errors as with #6723:

error: failed to update mingw32 (unable to lock database)
error: failed to update mingw64 (unable to lock database)
error: failed to update msys (unable to lock database)
error: failed to synchronize all databases

[Rastaban]

It looks like when the task is killed it does not free its lock on the database. Because we are reusing VMs in the CI system the lock is causing failures in unrelated PRs.

[grdowns]

We'll want to trigger a rebuild of all ports using vcpkg_acquire_msys before putting this change through. Thanks @emptyVoid!

[vicroms]

Waiting on CI results from #6760 where I added white-space changes to trigger CI builds of ports using MSYS.

[grdowns]

#6760 has finished and this PR is now passing Eager. Thanks again for this fix, @emptyVoid!