v2.0: CI: Disable downstream anchor builds (backport of #2629)

[mergify]

Problem

With solana-labs/solana-program-library#7148, spl-token-2022 has moved from using solana-zk-token-sdk to solana-zk-sdk, which is a major breaking change. Certain agave and anchor crates are depending on the re-export solana-zk-token-sdk in spl-token-2022, which is no longer present. This change is causing the downstream Anchor job to fail, since the patched version of spl-token-2022 is no longer compatible.

Summary of changes

Until new major versions of the SPL crates are available used by the Agave monorepo, disable the downstream anchor job.

---

This is an automatic backport of pull request #2629 done by Mergify.

[mergify]

Cherry-pick of 3b9e7a3 has failed:

On branch mergify/bp/v2.0/pr-2629
Your branch is up to date with 'origin/v2.0'.

You are currently cherry-picking commit 3b9e7a3ca5.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/workflows/downstream-project-anchor.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally