[DEV] Don't use .ONESHELL in Makefile (#5775)

I had used `.ONESHELL` to allow `cd` to effect the other commands, but
it seems this also prevents the error status from propagating from
anything but the last command in a rule.

e.g. see
#5673 (comment)

Makefile

@@ -28,27 +28,24 @@ test-cpp:
 	ninja -C $(BUILD_DIR) check-triton-unit-tests
 
 .PHONY: test-python
-.ONESHELL:
 test-unit: all
-	cd python/test/unit
-	$(PYTEST) -s -n 8 --ignore=cuda/test_flashattention.py --ignore=language/test_line_info.py --ignore=language/test_subprocess.py --ignore=test_debug.py
-	$(PYTEST) -s -n 8 language/test_subprocess.py
-	$(PYTEST) -s -n 8 test_debug.py --forked
-	TRITON_DISABLE_LINE_INFO=0 $(PYTEST) -s language/test_line_info.py
+	cd python/test/unit && $(PYTEST) -s -n 8 --ignore=cuda/test_flashattention.py \
+		--ignore=language/test_line_info.py --ignore=language/test_subprocess.py --ignore=test_debug.py
+	$(PYTEST) -s -n 8 python/test/unit/language/test_subprocess.py
+	$(PYTEST) -s -n 8 python/test/unit/test_debug.py --forked
+	TRITON_DISABLE_LINE_INFO=0 $(PYTEST) -s python/test/unit/language/test_line_info.py
 	# Run cuda/test_flashattention.py separately to avoid out of gpu memory
-	$(PYTEST) -s cuda/test_flashattention.py
-	TRITON_ALWAYS_COMPILE=1 TRITON_DISABLE_LINE_INFO=0 LLVM_PASS_PLUGIN_PATH=../../triton/instrumentation/libGPUInstrumentationTestLib.so \
-		$(PYTEST) --capture=tee-sys -rfs -vvv instrumentation/test_gpuhello.py
+	$(PYTEST) -s python/test/unit/cuda/test_flashattention.py
+	TRITON_ALWAYS_COMPILE=1 TRITON_DISABLE_LINE_INFO=0 LLVM_PASS_PLUGIN_PATH=python/triton/instrumentation/libGPUInstrumentationTestLib.so \
+		$(PYTEST) --capture=tee-sys -rfs -vvv python/test/unit/instrumentation/test_gpuhello.py
 
 .PHONY: test-regression
 test-regression: all
 	$(PYTEST) -s -n 8 python/test/regression
 
 .PHONY: test-interpret
-.ONESHELL:
 test-interpret: all
-	cd python/test/unit
-	TRITON_INTERPRET=1 $(PYTEST) -s -n 16 -m interpreter language/test_core.py language/test_standard.py \
+	cd python/test/unit && TRITON_INTERPRET=1 $(PYTEST) -s -n 16 -m interpreter language/test_core.py language/test_standard.py \
 		language/test_random.py language/test_block_pointer.py language/test_subprocess.py language/test_line_info.py \
 		runtime/test_autotuner.py::test_kwargs[False] \
 		../../tutorials/06-fused-attention.py::test_op --device=cpu