A few improvements to bazel ci scripts (#2076)
`aggregate_incompatible_flags_test_result.py`:
- Stripped out timestamps added by BuildKite in job log.
- Added support for collecting incompatible flag test result for
https://buildkite.com/bazel/bcr-bazel-compatibility-test
`bazelci.py`:
- Added support for overriding Bazel version in task config before task
expansion.
- Support `concurrency` and `concurrency_group` to limit CI resource
usage.
- Avoid hitting 429 Too Many Requests error while fetching a large
number of buildkite job logs.
2 files changed
