chore(librarian): bump gapic-generator to 1.28.3

[parthea]

1.28.3 is needed to resolve an issue where generation fails for libraries which don't contain samples. See https://github.com/googleapis/gapic-generator-python/releases/tag/v1.28.3 and googleapis/gapic-generator-python#2466

Generation failed for
google-apps-card
google-apps-script-type
google-cloud-alloydb-connectors
google-cloud-appengine-logging
google-cloud-bigquery-logging
google-cloud-common
google-cloud-iam-logging
google-cloud-source-context
google-geo-type
google-maps-places
google-shopping-type

The specific stack trace is

Broken 1 paths
nox > black docs google samples tests noxfile.py setup.py
Usage: black [OPTIONS] SRC ...
Try 'black -h' for help.

Error: Invalid value for 'SRC ...': Path 'samples' does not exist.
nox > Command black docs google samples tests noxfile.py setup.py failed with exit code 2

The reason that these libraries do not contain samples is that the APIs do not have any RPCs