Remove test.wgsl, add to .gitignore

Accidental commit of my test file for checking tint behavior.
Add to the .gitignore file so I don't accidentally check this in again.

Change-Id: Ie67f04cc307fa180d3a65d867a1777d008be8e17
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/70981
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>
diff --git a/.gitignore b/.gitignore
index 2b07d6f..91afea1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,7 +6,6 @@
 .vscode/*
 !.vscode/tasks.json
 .idea
-/build*/
 buildtools
 cmake-build-*/
 coverage.summary
@@ -25,3 +24,6 @@
 third_party/spirv-tools
 tools/clang
 tools/bin
+
+/build*/
+/test.wgsl