If you’re putting it in configuration.yaml you must have only one top-level (left-aligned) sensor: heading; and you’ll need to restart or reload template entities.
Also, your value_template line is wrong. Single-line templates need to be surrounded in quotes, and it’s recommended to use this format rather than the states object:
Invalid config for [sensor.template]: expected dictionary for dictionary value @ data['sensors']. Got None extra keys not allowed @ data['Friendly_name']. Got 'Akf Garage' extra keys not allowed @ data['climate_garage']. Got None extra keys not allowed @ data['unit_of_measurement']. Got '%' extra keys not allowed @ data['value_template']. Got "{{ state_attr('climate.room_12_garage', 'current_humidity') }}". (See ?, line ?).