re-enable Tint testing

Fix a typo in CMake variable naming

Change-Id: I46049669f5fdcf07cbfb2ec11ad99de212a8edc4
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35301
Commit-Queue: David Neto <dneto@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: David Neto <dneto@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/CMakeLists.txt

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d9636d8..3a48488 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -381,7 +381,7 @@
   target_link_options(libtint-fuzz PUBLIC -fsanitize=fuzzer -fsanitize-coverage=trace-cmp)
 endif()
 
-if(${TEST_BUILD_TESTS})
+if(${TINT_BUILD_TESTS})
   set(TINT_TEST_SRCS
     ast/array_accessor_expression_test.cc
     ast/assignment_statement_test.cc