freeipa.spec.in: remove python3-pexpect from Requires
    
    python3-pexpect will be removed in RHEL9.
    Update BuildRequires/Requires accordingly.
    
    Fixes: https://pagure.io/freeipa/issue/8938
    Signed-off-by: François Cami <fcami@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Antonio Torres <antorres@redhat.com>