builds: Try pushing to GHCR in parallel

Currently experiencing slow Dockerhub pulls: https://materializeinc.slack.com/archives/C01KV5PEZ9R/p1758540371320699

Author: def-

bin/ci-builder

@@ -125,6 +125,7 @@ build() {
         --build-arg "RUST_CPU_TARGET=$rust_cpu_target" \
         --build-arg "RUST_TARGET_FEATURES=$rust_target_features" \
         --tag materialize/ci-builder:"$tag" \
+        --tag ghcr.io/materialize/ci-builder:"$tag" \
         --tag materialize/ci-builder:"$cache_tag" \
         --target $docker_target \
         "$@" ci/builder

ci/builder/Dockerfile

@@ -345,7 +345,6 @@ RUN curl -fsSL https://amazon-inspector-sbomgen.s3.amazonaws.com/1.8.1/linux/$AR
 
 # Hardcode some known SSH hosts, or else SSH will ask whether the host is
 # trustworthy on the first connection.
-
 COPY ssh_known_hosts /etc/ssh/ssh_known_hosts
 
 ENV LDFLAGS="-fuse-ld=lld -static-libstdc++"
@@ -356,7 +355,7 @@ ENV CARGO_INCREMENTAL=1
 ENV HELM_PLUGINS=/usr/local/share/helm/plugins
 
 # Set up for a persistent volume to hold Cargo metadata, so that crate metadata
-# does not need to be refetched on every compile.
+# does not need to be refetched on every compilation.
 ENV CARGO_HOME=/cargo
 RUN mkdir /cargo && chmod 777 /cargo
 VOLUME /cargo

misc/python/materialize/mzbuild.py

@@ -786,11 +786,19 @@ def build(self, prep: dict[type[PreImage], Any], push: bool = False) -> None:
                 "-",
                 *(f"--build-arg={k}={v}" for k, v in build_args.items()),
                 "-t",
-                self.spec(),
+                f"docker.io/{self.spec()}",
+                "-t",
+                f"ghcr.io/materializeinc/{self.spec()}",
                 f"--platform=linux/{self.image.rd.arch.go_str()}",
                 str(self.image.path),
                 *(["--push"] if push else ["--load"]),
             ]
+
+        spawn.runv(
+            ["docker", "login", "ghcr.io", "-u", "materialize-bot", "--password-stdin"],
+            stdin=os.environ["GITHUB_GHCR_TOKEN"].encode(),
+        )
+
         spawn.runv(cmd, stdin=f, stdout=sys.stderr.buffer)
 
     def try_pull(self, max_retries: int) -> bool: