This uses python3 like autoninja{,.bat}.
https://source.chromium.org/chromium/chromium/tools/depot_tools/+/main:autoninja
https://source.chromium.org/chromium/chromium/tools/depot_tools/+/main:autoninja.bat

Fixed: 1203012
Change-Id: I4daf1892024358c5b7d88b1e32b15c82cb4411d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2968069
Commit-Queue: Dirk Pranke <dpranke@google.com>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>