Disable auto line ending conversion in Windows Dockerfiles

[aknuds1]

We (Grafana Labs) have been having test failures on Windows due to automatic conversion of line endings to CRLF on Windows. I tracked it down to being caused by the Git config parameter core.autocrlf being set to true in the Windows Docker image of the Drone Git plugin. This PR proposes to disable the parameter, so line endings aren't altered by Git on checkout.

I tested the image and it solves our issue.