chore: Update gapic-generator-python to v1.11.8

PiperOrigin-RevId: 574178735

Author: Google APIs

WORKSPACE

@@ -324,7 +324,7 @@ load("@rules_gapic//python:py_gapic_repositories.bzl", "py_gapic_repositories")
 
 py_gapic_repositories()
 
-_gapic_generator_python_version = "1.11.7"
+_gapic_generator_python_version = "1.11.8"
 
 http_archive(
     name = "gapic_generator_python",