Update configuring-playbook-bridge-mautrix-meta-messenger.md

[ThellraAK]

Add " ' " around the username for matrix_admin.

[spantaleev]

Why? Are you using a username with special characters that break the YAML parser without quotes?

[ThellraAK]

Without the single quotes I get an error

ERROR! We were unable to read either as JSON nor YAML, these are the errors we got from each:
JSON: Expecting value: line 1 column 1 (char 0)

Syntax Error while loading YAML.
  found character that cannot start any token

The error appears to be in '/share/matrix-docker-ansible-deploy/inventory/host_vars/matrix.relativelyprivate.com/vars.yml': line 58, column 15, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

matrix_mautrix_meta_messenger_enabled: true
matrix_admin: @ThellraAK:mydomain.com
              ^ here

That's with matrix_admin: @ThellraAK:mydomain.com

However with matrix_admin: '@ThellraAK:mydomain.com'

It works as expected.