fix: support remote arm64 builds, as well (#9018)

BUILD.bazel

@@ -11,21 +11,9 @@ platform(
     ],
 )
 
-platform(
+alias(
     name = "rbe",
-    constraint_values = [
-        "@platforms//cpu:x86_64",
-        "@platforms//os:linux",
-        "@bazel_tools//tools/cpp:clang",
-        "@toolchains_llvm_bootstrapped//constraints/libc:gnu.2.28",
-    ],
-    exec_properties = {
-        # Ubuntu-based image that includes git, python3, dotslash, and other
-        # tools that various integration tests need.
-        # Verify at https://hub.docker.com/layers/mbolin491/codex-bazel/latest/images/sha256:8c9ff94187ea7c08a31e9a81f5fe8046ea3972a6768983c955c4079fa30567fb
-        "container-image": "docker://docker.io/mbolin491/codex-bazel@sha256:8c9ff94187ea7c08a31e9a81f5fe8046ea3972a6768983c955c4079fa30567fb",
-        "OSFamily": "Linux",
-    },
+    actual = "@rbe_platform",
 )
 
 exports_files(["AGENTS.md"])