CI: Disable downstream anchor builds (anza-xyz#2629)

#### 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.

.github/workflows/downstream-project-anchor.yml

@@ -42,6 +42,7 @@ jobs:
     strategy:
       matrix:
         version: ["master"]
+    if: false # Re-enable once new major versions for spl-token-2022 and spl-pod are out
     steps:
       - uses: actions/checkout@v4