fix: Add shopt -s nullglob to dependencies script (#1130) (#4)

* fix: Add `shopt -s nullglob` to dependencies script (#1130)

This prevents processing the unexpanded glob "**/.flattened-pom.xml" in repos which do not flatten any POMs.
Source-Link: googleapis/synthtool@87254ac
Post-Processor: gcr.io/repo-automation-bots/owlbot-java:latest@sha256:a9b83a276c82987d284b733713fe86a3c8a2cc457933767eeb2688b882e54c6a

* 🦉 Updates from OwlBot

See https://github.com/googleapis/repo-automation-bots/blob/master/packages/owl-bot/README.md

* chore: rebase branch

* chore: ignore unused dependency

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Neenu Shaji <Neenu1995@users.noreply.github.com>
Co-authored-by: Neenu1995 <neenushaji@google.com>

Author: gcf-owl-bot[bot]