update bazel-toolchains pin to latest release
Part of changes to allow bazelci to use 0.19.0 configs.
RBE toolchain configs at or before 0.17.0 are not compatible with bazel 0.19.0 or above.

PiperOrigin-RevId: 220085357
diff --git a/WORKSPACE b/WORKSPACE
index e79c42b..f608cf2 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -163,11 +163,11 @@
 
 http_archive(
     name = "bazel_toolchains",
-    sha256 = "cefb6ccf86ca592baaa029bcef04148593c0efe8f734542f10293ea58f170715",
-    strip_prefix = "bazel-toolchains-cdea5b8675914d0a354d89f108de5d28e54e0edc",
+    sha256 = "fa1459abc7d89db728da424176f5f424e78cb8ad7a3d03d8bfa0c5c4a56b7398",
+    strip_prefix = "bazel-toolchains-42619b5476b7c8a2f5117f127d5772cc46da2d1d",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/cdea5b8675914d0a354d89f108de5d28e54e0edc.tar.gz",
-        "https://github.com/bazelbuild/bazel-toolchains/archive/cdea5b8675914d0a354d89f108de5d28e54e0edc.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/42619b5476b7c8a2f5117f127d5772cc46da2d1d.tar.gz",
+        "https://github.com/bazelbuild/bazel-toolchains/archive/42619b5476b7c8a2f5117f127d5772cc46da2d1d.tar.gz",
     ],
 )