registration key does not get set if there is an empty line

[Anna Savchenko]

When setting the registration key through the file, juju introduces an empty line in the configuration. Eventually, the registration key doesn't get set on landscape server.

Bundle:
vars:
  - &registration-key include-file://../../secrets/landscape-registrationkey
applications:
  landscape-server:
    charm: landscape-server
    num_units: 3
    options:
      registration_key: *registration-key

$ cat secrets/landscape-registrationkey
landscapekey
<no new line>

$juju config landscape-client registration-key
landscapekey
<new line>

$ juju config -m landscape landscape-server registration_key
landscapekey
<new line>

The new line is also present in /etc/landscape/client.conf.

Landscape server version: 23.03
Charm revision: 102