Another attempt to fix failing `gn check --check` in Chromium

Change-Id: I6d1690e5c6f8a4b0a8c5265cd3713698f0ee7cab
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48660
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/BUILD.gn

diff --git a/test/BUILD.gn b/test/BUILD.gn
index 6b4a159..ae2fe55 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -108,6 +108,8 @@
 }
 
 source_set("tint_test_helpers") {
+  testonly = true
+
   sources = [
     "../src/ast/intrinsic_texture_helper_test.cc",
     "../src/ast/intrinsic_texture_helper_test.h",
@@ -128,6 +130,11 @@
   }
 
   configs += [ ":tint_unittests_config" ]
+
+  public_deps = [
+    ":gmock_and_gtest",
+    "${tint_root_dir}/src:libtint",
+  ]
 }
 
 template("tint_unittests_source_set") {
@@ -148,11 +155,7 @@
     if (!defined(invoker.deps)) {
       deps = []
     }
-    deps += [
-      ":gmock_and_gtest",
-      ":tint_test_helpers",
-      "${tint_root_dir}/src:libtint_core_src",
-    ]
+    deps += [ ":tint_test_helpers" ]
   }
 }