test: suppress .pyc writeback in bazel test runs

Bazel tests cd into their source directory before running, so importing
a shared helper (helpers.py, ppl_aux.py, ...) made CPython write
__pycache__/*.pyc files back into the source tree during the action.
Bazel's --guard_against_concurrent_changes then detected the mid-action
modification and skipped caching the result, emitting many
"Skipping uploading outputs because of concurrent modifications"
warnings and forcing those tests to re-run every invocation.

Set PYTHONDONTWRITEBYTECODE=1 in the bazel-only test wrapper so no
bytecode is written, eliminating the warnings and restoring caching.

Signed-off-by: Matt Liberty <mliberty@precisioninno.com>

Author: maliberty

test/bazel_test.sh

@@ -9,6 +9,12 @@ export RESULTS_DIR="${TEST_UNDECLARED_OUTPUTS_DIR}/results"
 export REGRESSION_TEST=$(realpath $REGRESSION_TEST)
 if [ -n "${TEST_SRCDIR:-}" ]; then
 	export BAZEL_TEST=1
+	# Tests cd into their source directory, so importing a shared helper
+	# (helpers.py, ppl_aux.py, ...) makes CPython write __pycache__ .pyc
+	# files back into the source tree mid-action. Bazel then sees a
+	# concurrent modification and skips caching the result
+	# (--guard_against_concurrent_changes). Suppress bytecode writing.
+	export PYTHONDONTWRITEBYTECODE=1
 	workspace_root="${TEST_SRCDIR}/${TEST_WORKSPACE:-_main}"
 	python_paths="${workspace_root}"
 	if [ -d "${workspace_root}/python" ]; then