chore(librarian): update gapic-generator to 1.30.11 (#16078)

This is needed to resolve
googleapis/gapic-generator-python#2579 and
unblock #16063

Author: parthea

.generator/requirements.in

@@ -1,5 +1,5 @@
 click
-gapic-generator==1.30.10 # Allow protobuf 7.x https://github.com/googleapis/gapic-generator-python/pull/2575
+gapic-generator==1.30.11 # Downgrade mypy https://github.com/googleapis/gapic-generator-python/pull/2580
 nox
 starlark-pyo3>=2025.1
 build