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

WORKSPACE

@@ -168,11 +168,11 @@ http_file(
 
 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",
     ],
 )