[sdk generation pipeline] update command for changelog generation (#41688)

* update for tox run

* update log

Author: msyyc

tools/azure-sdk-tools/packaging_tools/package_utils.py

@@ -29,7 +29,7 @@ def create_package(prefolder, name, dest_folder=DEFAULT_DEST_FOLDER):
 @return_origin_path
 def change_log_new(package_folder: str, lastest_pypi_version: bool) -> str:
     os.chdir(package_folder)
-    cmd = "tox run -c ../../../eng/tox/tox.ini --root . -e breaking --  --changelog "
+    cmd = "python -m tox run -c ../../../eng/tox/tox.ini --root . -e breaking --  --changelog "
     if lastest_pypi_version:
         cmd += "--latest-pypi-version"
     try:
@@ -40,8 +40,11 @@ def change_log_new(package_folder: str, lastest_pypi_version: bool) -> str:
         raise e
     _LOGGER.info(f"Breaking change detector output: {output}")
     result = [l for l in output.split("\n")]
-    begin = result.index("===== changelog start =====")
-    end = result.index("===== changelog end =====")
+    try:
+        begin = result.index("===== changelog start =====")
+        end = result.index("===== changelog end =====")
+    except ValueError:
+        raise Exception("\n".join(result))
     return "\n".join(result[begin + 1 : end]).strip()