chore: update to gapic-generator-python 1.5.0

feat: add support for `google.cloud.<api>.__version__`
PiperOrigin-RevId: 484665853

Author: Google APIs

WORKSPACE

@@ -292,7 +292,7 @@ load("@rules_python//python:pip.bzl", "pip_install")
 
 pip_install()
 
-_gapic_generator_python_version = "1.4.4"
+_gapic_generator_python_version = "1.5.0"
 
 http_archive(
     name = "gapic_generator_python",