Wildcards in condition checks

Configuration
1

I’m trying to achieve the following:

When I press a button and a certain channel on my media player is active, switch to a certain channel.
So, the trigger is the press of a button and the condition the state of the media player.

trigger:
  - device_id: acdc951e0ae411eb9baccd9b5879f7a5
    domain: deconz
    platform: device
    type: remote_button_long_press
    subtype: dim_up
condition:
  - condition: template
    value_template: >-
      {{ (state_attr('media_player.sonos_kleines_bad', 'media_channel')) in 'Deutschlandfunk' }}
action:
  - service: media_player.select_source
    data:
      source: ROCK ANTENNE Heavy Metal
    target:
      entity_id: media_player.sonos_kuche
mode: single

That works, as long as the media_player returns “Deutschlandfunk” exactly.
But sometimes it returns “Deutschlandfunk - Nachrichten” or the like. And then this check fails.

So, what I essentially need, is some wildcard functionality to achieve that.

I already tried:

{{ 'Deutschlandfunk' in states('media_player.sonos_kleines_bad') }}
{{ 'Deutschlandfunk' in states('media_player.sonos_kleines_bad.media_channel') }}

but both return “false”.

When I check the entity itself, it returns the following:
media_channel: Deutschlandfunk

I really do not understand the documentation and thus do not know how to do it right.

2 
{{ 'Deutschlandfunk' in states('media_player.sonos_kleines_bad.media_channel') }}

Should be

{{ 'Deutschlandfunk' in state_attr('media_player.sonos_kleines_bad','media_channel') }}