Publish binaries to the centos7 bucket, again (#2296)

Old versions of Bazelisk are still using this bucket to download general
Linux binaries.

This change is a temporary workaround - we should stop publishing to
this bucket in the future, especially since its name is misleading as we
build all Linux binaries on Rocky Linux 8 now.

Progress towards
#2294

Author: fweikert

buildkite/bazelci.py

@@ -292,8 +292,9 @@
         "emoji-name": ":rocky: Rocky Linux 8",
         # We publish to the ubuntu1404 bucket since all Python versions of
         # Bazelisk <= v1.26.0 download from this bucket on Linux.
-        # We should delete it after a migration period.
-        "publish_binary": ["ubuntu1404", "linux"],
+        # Same problem for the centos7 bucket and Go-Bazelisk older than v1.21.0.
+        # We should stop doing this after a migration period.
+        "publish_binary": ["centos7", "ubuntu1404", "linux"],
         "docker-image": f"gcr.io/{DOCKER_REGISTRY_PREFIX}/rockylinux8",
         "python": "python3.8",
     },