`buildx.Build` doesn't terminate if context is canceled, so this PR
rearranges things such that we can wait for the build or context to
finish.
Fixes#533.
**Description:**
This PR updates the `moby/buildkit` dependency to `v0.20.1` in order to
remain compatible with recent changes required by GitHub Actions (GHA)
caching.
During the upgrade, several upstream behavioral changes required forking
and restoring legacy logic to maintain compatibility:
- Introduced `containsGithubToken` to replicate logic that was
previously in `buildflags.ParseCacheEntry`, which is now removed. This
check ensures we return `nil` instead of a zero-value object.
- Forked the previous implementation of `ParseExports`, as its upstream
logic changed significantly. This ensures short-term compatibility for
release before the GHA deprecation deadline.
- A follow-up issue will be created to improve this forked logic and
align more closely with upstream behavior.
🚨 **Fixes critical issue:**
This change addresses a high-priority issue where GitHub Actions cache
will stop working due to the upcoming deprecation of the legacy caching
service (effective **April 15, 2025**).
Recent build failures showed errors like:
> *"This legacy service is shutting down, effective April 15, 2025.
Migrate to the new service ASAP. For more information:
https://gh.io/gha-cache-sunset"*
Root cause was identified in #515, where using `buildx >= 0.21.0` is
required.
This repo was previously using `buildx 0.18.0`.
Closes: #515
