This PR is trying to improve the tests by various ways:

• Update README.md with information how to run the tests on your fork and branch using containers
• Update README.md with information about how to run tox tests locally
• All the tests on CentOS 8 Stream CI container are passing
• Update Fedora CI containers to F35
  • 7 tests are still failing for rpms container with following reasons:
    • tests/test_pagure_flask_ui_repo.py::PagureFlaskRepotests (2 tests) - Fork of the fork is recognized as project
    • tests/test_pagure_lib_git_auth.py::PagureLibGitAuthtests (2 tests) - The string is split by SQLAlchemy warnings about relationship. Should we ignore them?
    • tests/test_pagure_flask_api.py::PagureFlaskApitests::test_api_get_request_data - Need to have flask 2.0.2 to work properly, this isn't available in F35 yet, but it's in F36
    • tests/test_pagure_flask_dump_load_ticket.py::PagureFlaskDumpLoadTicketTests::test_dumping_reloading_ticket - Pygit 2 doesn't support latest arrow library. See https://github.com/libgit2/pygit2/issues/1122
    • Black formatting is different
  • 40 tests failing for pip CI container

I will try to work on the tests a little more. But this is ready to be merged.