gitlab-ci: Fix hadrian bootstrapping of release pipelines

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.