On Windows, scripts on the current directory take precedence over PATH, so
that when testing depot_tools on Windows, calling `vpython.bat` will
execute the copy of vpython of the depot_tools under test instead of the
one in the bot.
As a workaround, we run the tests from the parent directory instead.

Change-Id: I5187943b6cf7499d50b3f1a2ec906a5e8fd84835
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1910448Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>