Previously we would attempt to test hadrian bootstrapping in the
validate build flavour. However, ci.sh refuses to run validation
builds during release pipelines, resulting in job failures. Fix this by
testing bootstrapping in the release flavour during release pipelines.
We also attempted to record perf notes for these builds, which is redundant work and undesirable now since we no longer build in a consistent flavour.
Forward port of ddf6c670.