fix: flask-wtf csrf validation requires timestamp
    
    Since v0.14 the csrf lifetime and validation in flask-wtf is based on timestamps.
    Test 'tests/test_pagure_flask_form.py' failed because a date was used if flask-wtf version > 0.10.0.
    For backward compatibility, a date is still used for flask-wtf versions >=0.10.0 and < 0.14.0
    
    Reference:
    https://flask-wtf.readthedocs.io/en/latest/changes/#version-0-14