chore(python): support multiple codeowners in blunderbuss#1124

gcf-owl-bot[bot] wants to merge 1 commit intomaingoogleapis/python-spanner:mainfrom

owl-bot-update-lock-704d34f7c25e15fcb12ac19af08eb7cf01eabc16fb4781590223e01dd252985egoogleapis/python-spanner:owl-bot-update-lock-704d34f7c25e15fcb12ac19af08eb7cf01eabc16fb4781590223e01dd252985eCopy head branch name to clipboard