chore: Update gapic-generator-python to v1.8.4

Google APIs · copybara-github · commit 64cf8492b217 · 2023-02-07T09:48:09.000-08:00
PiperOrigin-RevId: 507808936
diff --git a/WORKSPACE b/WORKSPACE
@@ -316,7 +316,7 @@ load("@rules_python//python:pip.bzl", "pip_install")
 
 pip_install()
 
-_gapic_generator_python_version = "1.8.3"
+_gapic_generator_python_version = "1.8.4"
 
 http_archive(
     name = "gapic_generator_python",
