fix(Makefile): narrow TORCH_GROUP override to the setup_env.sh call only

`export TORCH_GROUP=torch_2_X && ...` set the variable for the whole
recipe's shell, which happened to be harmless since nothing else in
these three recipes reads TORCH_GROUP, but the intent was always to
scope the override to just the one setup_env.sh invocation that needs
it. Using `TORCH_GROUP=torch_2_X <command>` as an inline prefix does
that precisely: it applies only to the first command in the `&&`
chain, reverting to the Makefile's own default/command-line value for
everything after.

Author: guru-desh

Makefile

@@ -181,8 +181,7 @@ env: _maybe_patch_pyproject
 
 # Set up development environment with latest supported PyTorch version
 env-highest-torch: _maybe_patch_pyproject
-	@export TORCH_GROUP=torch_2_11 && \
-	$(SETUP_ENV) --venv $(VENV_HIGHEST_TORCH) --python-version $(PYTHON_VERSION)
+	@TORCH_GROUP=torch_2_11 $(SETUP_ENV) --venv $(VENV_HIGHEST_TORCH) --python-version $(PYTHON_VERSION)
 	@$(call write_active_venv,$(VENV_HIGHEST_TORCH))
 
 # Set up environment for running tutorials (quantization notebook)
@@ -251,8 +250,7 @@ test-smoke:
 # Run tests on lowest supported PyTorch version (pass PYTEST_ARGS for custom flags)
 test-lowest-pytorch:
 	@echo "Running tests on lowest PyTorch version supported..."
-	@export TORCH_GROUP=torch_2_8 && \
-	$(call use_env,VENV_LOWEST_TORCH) && \
+	@TORCH_GROUP=torch_2_8 $(call use_env,VENV_LOWEST_TORCH) && \
 	echo "Testing with lowest supported PyTorch versions" && \
 	uv run --no-sync --active python $(SCRIPTS)/make/log_versions.py && \
 	$(RUN_TESTS) $(PYTEST_ARGS) && \
@@ -261,8 +259,7 @@ test-lowest-pytorch:
 # Run tests on highest supported PyTorch version (pass PYTEST_ARGS for custom flags)
 test-highest-pytorch:
 	@echo "Running tests on highest PyTorch version supported..."
-	@export TORCH_GROUP=torch_2_11 && \
-	$(call use_env,VENV_HIGHEST_TORCH) && \
+	@TORCH_GROUP=torch_2_11 $(call use_env,VENV_HIGHEST_TORCH) && \
 	echo "Testing with latest supported PyTorch versions" && \
 	uv run --no-sync --active python $(SCRIPTS)/make/log_versions.py && \
 	$(RUN_TESTS) $(PYTEST_ARGS) && \