Bump imap-tools from 1.7.2 to 1.7.3 in /docker/py3-tools-ubi

Bumps [imap-tools](https://github.com/ikvk/imap_tools) from 1.7.2 to 1.7.3.
- [Release notes](https://github.com/ikvk/imap_tools/releases)
- [Changelog](https://github.com/ikvk/imap_tools/blob/master/docs/release_notes.rst)
- [Commits](ikvk/imap_tools@v1.7.2...v1.7.3)

---
updated-dependencies:
- dependency-name: imap-tools
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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