Use python3 instead of python for bootstrap * In roll_aosp.sh, replaced the remaining python usage with python3. Bug: b/246559064 Change-Id: Iea9737376c34264fec5d60e4cb772eb8c5be81f2 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5494462 Reviewed-by: Roman Lavrov <romanl@google.com> Auto-Submit: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Roman Lavrov <romanl@google.com>