py-flask-babel: update to 3.1.0

v3.1.0
- Documentation and packaging improvements.
- Don't return the default locale twice
- Fix tests breaking against babel 12.2, which changed localized times to use
  non-breaking-spaces. Babel 12.2 or greater is now required.
- Relax version requirements for dependencies.

v3.0.0
Major version bump as this version removes support for Python 3.5 and 3.6, along with multiple
major breaking changes. Hope you've been following SemVer :)

- Dropped support for end-of-life Python 3.5 and 3.6, added tests for 3.10 and 3.11.
- Fixes to documentation to address outdated links and settings
- Jinja version 3 or greater is now required (released 2021)
- Removed Babel._date_formats, use the public Babel.date_formats instead.
- list_translations() always returns the default locale, even if it does not exist.
- Add lazy_npgettext()
- Babel.locale_selector and Babel.timezone_selector no longer exist. They must be provided
  either when the Babel() object is created or when init_app() is called. This is to support
  having a single Babel object for multiple Flask apps as well as to simplify settings
  and multi-threaded state.
- Most configuration options can be passed directly through init_app().

v2.0.0
Starting with version 2, flask-babel drops official support for Python2.
Python versions 3.5 through 3.9-beta1 are tested and supported, as well as pypy3.

- Tests moved from unittest to pytest
- Domain and caching support from Flask-BabelEx
- Documentation moved from python-hosted to Github Pages.
- CI moved from Travisci to Github Actions
- Small documentation improvements.
- Removed uncessary checks on get_translations()
- localeselector and timezoneselector can be changed after creation.


(markd)