ci migrate: hasCustomRunsOn treats depot-ubuntu-latest as a custom label #578

hasCustomRunsOn in pkg/ci/compat/analyze.go does not agree with MapLabel / GitHubToDepotRunner in pkg/ci/migrate/runslabel.go (main d58b6be).

Transform writes hyphenated labels (ubuntu-latest → depot-ubuntu-latest). Analyze only skips ubuntu-latest and underscore depot_ubuntu_latest / prefix depot_. So a job that is already Depot-native, or a mapped ubuntu-24.04, is reported as runs-on (custom labels) Partial.

Repro on d58b6be (helper is unexported; same predicates):

• ubuntu-latest → not custom
• depot-ubuntu-latest → custom (should be native)
• ubuntu-24.04 → custom (standard GH map key)
• depot_ubuntu_latest → not custom (label the mapper never emits)

JobFeatureRules["runs-on (custom labels)"] Note/Suggestion also say depot_ubuntu_latest. Docs and runslabel.go use depot-ubuntu-latest.

No test covers hasCustomRunsOn. TestAnalyzeJobsMatrixSelfHostedUnsupported only asserts the matrix+self-hosted issue; the extra issue is ubuntu-latest,self-hosted hitting custom via self-hosted.

Tiny leaf: treat migrate.ClassifyLabel / GitHubToDepotRunner as the allowlist (hyphen depot- prefix + the four ubuntu-* keys), keep expressions skipped, keep unknown labels Partial, add table tests. Not a product change.

I am not opening a PR.