Fix Kokoro Windows build

Make sure .bat files are checked out as CRLF, otherwise goto will jump
to the wrong offset under certain conditions.

Change-Id: Iffaf2ec960890ed7f0f8bb9b62bb7724d8334941
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/131981
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

.gitattributes

@@ -9,3 +9,4 @@
 *.wgsl   eol=lf
 *.h      eol=lf
 *.cpp    eol=lf
+*.bat    eol=crlf