GHA/windows: change openssh server, non-debug-enabled MSVC job, other improvements

GHA/windows: change openssh server, non-debug-enabled MSVC job, other improvements

MSVC:

- switch jobs to standard openssh server. Reduce exceptions.
- make the SCP/SFTP ignore list more specific and comment with details.
- keep using OpenSSH-Windows for the OpenSSL job, and bump to the
  prerelease version.
- disable `ENABLE_DEBUG` for BoringSSL to have such build tested. (This
  is the first Windows non-ENABLE_DEBUG build with test runs.)

Takeaways:

- test 612 broken on Windows.
- test 613 broken on Windows with the standard openssh server.
- test 614 broken with libssh and OpenSSH-Windows.
- test 3022 broken with libssh2 and OpenSSH-Windows.
- tests broken with OpenSSH-Windows:
  601 603 617 619 621 641 665 2004.
- vcpkg `libssh2[core,zlib]` broken due to:
  curl: (67) Authentication failure

MSVC prep steps:

- install base msys2 package to simplify configuration, align with other
  jobs and allow to use msys2 packages for tests.
- add support for msys2 openssh server. Keep OpenSSH-Windows as per-job
  option. Add support for OpenSSH prerelease versions.
  Prerelease does not make a difference in test results, but, stable was
  last updated in 2019 (v8.0.0.1) and it seems better to use maintained
  release track, with its latest from April 2024 (v9.5.0).
  https://community.chocolatey.org/packages/openssh/8.0.0.1
  https://community.chocolatey.org/packages/openssh
  https://github.com/PowerShell/Win32-OpenSSH
  https://github.com/PowerShell/openssh-portable
- add 'libssh' to its job name.
- make `ENABLE_DEBUG` a per-job option.

msys/mingw:

- install `openssh` later and only when necessary.
- downgrade msys2 runtime later. (to follow other jobs)
- disable `CheckSpace` earlier. Also to untie it from the runtime
  downgrade step, which we would hopefully drop.

Closes #16672