Incompatible with Flask v3

[xenophonf]

With the latest version of Flask installed (e.g., version 3.0.3), Python signals an import error when importing Flask-FomanticUI:

src/app.py:24: in <module>
    from flask_fomanticui import FomanticUI
.venv/lib/python3.11/site-packages/flask_fomanticui/__init__.py:35: in <module>
    from .core import *  # noqa
.venv/lib/python3.11/site-packages/flask_fomanticui/core.py:32: in <module>
    from flask import Blueprint, Markup, current_app, url_for
E   ImportError: cannot import name 'Markup' from 'flask' (.venv/lib/python3.11/site-packages/flask/__init__.py)

Cf. https://github.com/pallets/flask/issues/5353#issuecomment-1839195620