build: update bazel_toolchains to version 0.28.4 (#15319)

Author: renovate-bot

WORKSPACE

@@ -108,9 +108,9 @@ web_test_repositories()
 # Bring in bazel_toolchains for RBE setup configuration.
 http_archive(
     name = "bazel_toolchains",
-    sha256 = "dcb58e7e5f0b4da54c6c5f8ebc65e63fcfb37414466010cf82ceff912162296e",
-    strip_prefix = "bazel-toolchains-0.28.2",
-    url = "https://github.com/bazelbuild/bazel-toolchains/archive/0.28.2.tar.gz",
+    sha256 = "e71eadcfcbdb47b4b740eb48b32ca4226e36aabc425d035a18dd40c2dda808c1",
+    strip_prefix = "bazel-toolchains-0.28.4",
+    url = "https://github.com/bazelbuild/bazel-toolchains/archive/0.28.4.tar.gz",
 )
 
 load("@bazel_toolchains//rules:environments.bzl", "clang_env")