Add optional ignore_case param to wait_for_strings

[summersamara]

Motivation:

While trying to build python-redis-lock
on NixOS with redis-server version 7.2.5
the tests kept failing at wait_for_strings assertion on the output of redis-server, because the redis-server was outputting:
Ready to accept connections
instead of
ready to accept connections (different string case)

# python-redis-lock: tests/conftest.py
    with TestProcess(
        'redis-server', '--port', '0', '--save', '', '--appendonly', 'yes', '--dir', tmp_path, '--unixsocket', redis_socket
    ) as redis_server:
        wait_for_strings(redis_server.read, 2, 'ready to accept connections')

I would also create a PR in parallel to this one, in python-redis-lock repository, to make use of the change proposed in this PR in case it got approved and released.