Update VM base image from Windows 10 build 1909 to build 20H2.
Update VM base image from Windows 10 build 1909 to build 20H2.

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration