fix(ci): add _sanitize_a2a to TOP_LEVEL_MODULES allowlist (third workflow defect)

Run 5160 publish-runtime build step failed:

  error: TOP_LEVEL_MODULES drifted from workspace/*.py contents:
    in workspace/ but NOT in TOP_LEVEL_MODULES (will ship un-rewritten): ['_sanitize_a2a']
    Edit scripts/build_runtime_package.py:TOP_LEVEL_MODULES to match.

workspace/_sanitize_a2a.py was added recently but the allowlist in
scripts/build_runtime_package.py was not updated. The build script
intentionally aborts (exit 3) when it detects the drift, because
shipping a module un-rewritten breaks the package's flat-layout import
contract.

Fix: add '_sanitize_a2a' to the set. Alphabetical order preserved
(it sorts before 'a2a_*').

Third workflow defect after #353 (workflow_dispatch.inputs parser) and
#355 (Publish step working-directory). After this lands, attempt #4 of
runtime-v0.1.130 should finally succeed.

Refs: #351, #353, #355, #348 Q3

scripts/build_runtime_package.py

@@ -50,6 +50,7 @@ from pathlib import Path
 # without updating this set), which broke every workspace startup with
 # `ModuleNotFoundError: No module named 'transcript_auth'`.
 TOP_LEVEL_MODULES = {
+    "_sanitize_a2a",
     "a2a_cli",
     "a2a_client",
     "a2a_executor",