ci: Re-enable bootc revdep CI

[cgwalters-bot]

Release 0.7.0 (469f6d6) disabled the bootc reverse dependency job "until bootc main updates", pinning it to the cgwalters/bootc adapt-composefs-rs-v1-erofs-2 branch in the meantime. That branch has now landed as bootc-dev/bootc#2248. bootc main depends on composefs-rs by git tag v0.9.2, and our workspace version is still 0.9.2, so the [patch] override in bootc/Justfile applies to it again. This re-enables the job against bootc main, the same way 6b026f4 did the last time.

It also fixes a side effect of the disable: never() isn't a valid Actions expression function, so the workflow file failed to parse. As a result, every push to any branch (including gh-readonly-queue/* and Renovate branches) recorded a failed run with no jobs. The workflow now has 1000+ such runs.

Alternatives considered

• Keep it disabled and fix only the expression. That means if: false, or dropping the automatic triggers and keeping workflow_dispatch. An earlier version of this branch did the latter. Now that bootc main has caught up, that would just keep the test off for no reason.
• Label-gate it (e.g. run on PRs only with a ci/bootc label, as proposed for bootc's operator revdep job). The job isn't part of required-checks, so a failure doesn't block merging. Before 0.7.0 it ran on every PR, so this keeps it that way. Gating is easy to add later if the ~2h runs turn out to be too costly.

Testing

• actionlint: the undefined function "never" error is gone. The remaining output is two shellcheck infos in the pre-existing "Install tmt" step.
• Exercised on a fork (cgwalters-forge/composefs-rs):
  • Pushing this branch recorded no push-event run of this workflow (it only triggers on pushes to main now that the file parses). For comparison, pushes of another branch based on current main to the same fork each recorded a failed 0-job run, e.g. https://github.com/cgwalters-forge/composefs-rs/actions/runs/35946914814.
  • Opening the PR triggered a real pull_request run against bootc main: https://github.com/cgwalters-forge/composefs-rs/actions/runs/35947623278. It passed in 42 minutes: bootc main at 41049cca was built with this tree patched in (bootc patched for composefs-rs at b020175, all composefs crates compiled from the local path), and both tmt plans passed (plan-01-readonly, plan-24-image-upgrade-reboot, sealed UKI + systemd-boot). workflow_dispatch wasn't exercised separately; it is unchanged.

Generated-by: https://github.com/cgwalters/#llms

[cgwalters]

@cgwalters-bot add my signoff

[cgwalters-bot]

Added your sign-off (promote now also signs off where the DCO app runs); same for #401.

Generated-by: https://github.com/cgwalters/#llms