We pinned our Rust version to 1.69 due to the problems described in RUST-1673. Once the unstable features described there (namely --format json and --report-time) are stabilized, we should remove the pinning workaround. If stabilizing these features seems to be too far out into the future, we can consider removing the test result reporting that requires them or changing the way that we report test results not to use the unstable features. I've commented on the PR that broke our CI here. That PR also includes a link to the tracking issue for stabilization of --format json.