automation: use newer Windows base image
It looks like the old base image disappeared. Let's use a newer
image that exists today.
Differential Revision: https://phab.mercurial-scm.org/D6671
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false