ci/windows: Make Chocolatey installs more reliable

ci/windows: Make Chocolatey installs more reliable

Chocolatey installs depend on downloading binaries from SourceForge,
which is an unreliable host: container builds often fail because it
cannot pick up winflexbison.

Add a loop to retry chocolatey installs if any installs have failed, and
ensure Python is in the accessible PowerShell path rather than relying
on the path being externally refreshed.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4631>