[UnitTest] Removed vulkan from CI run of task_python_topi.sh

Vulkan unit tests were enabled with
apache#9093, but were only intended to run
tests/python/unittest/test_target_codegen_vulkan.py.  Since
task_python_topi.sh did not explicitly specify `TVM_TEST_TARGETS`, it
defaulted to `tvm.testing.utils.DEFAULT_TEST_TARGETS`, which includes
the vulkan runtime.

This commit adds an explicit specification of `TVM_TEST_TARGETS` for
the topi unit tests, matching the targets enabled in the CI GPU build,
but excluding vulkan.

tests/scripts/task_python_topi.sh

@@ -21,6 +21,8 @@ set -u
 
 source tests/scripts/setup-pytest-env.sh
 
+export TVM_TEST_TARGETS="llvm; llvm -device=arm_cpu; cuda; cuda -model=unknown -libs=cudnn"
+
 # to avoid CI thread throttling.
 export TVM_BIND_THREADS=0
 export OMP_NUM_THREADS=1