Symfony framework.yaml invalid YAML - but it's not? - symfony

Question

I've started getting this error...not sure why or how?
Here is the framework.yaml:
security:
# https://symfony.com/doc/current/security.html#where-do-users-come-from-user-providers
providers:
ad_ldap:
ldap:
service: Symfony\Component\Ldap\Ldap
base_dn: dc=mydomain,dc=local
search_dn: 'appuser'
search_password: "xxx"
default_roles: ROLE_USER
uid_key: 'sAMAccountName'
filter: '({uid_key}={username})'
Giving me this error:
In FileLoader.php line 180:
The file "/vagrant/project/config/packages/security.yaml" does not
contain valid YAML: Unexpected characters near "rname})' " at
line 12 (near "filter: '({uid_key}={us ername})' ") in
/vagrant/project/config/packages/security.yaml (which is loaded in
resource "/vagrant/project/config/packages/security.yaml").
In YamlFileLoader.php line 693:
The file "/vagrant/project/config/packages/security.yaml" does not
contain valid YAML: Unexpected characters near "rname})' " at
line 12 (near "filter: '({uid_key}={us ername})' ").
In Parser.php line 760:
Unexpected characters near "rname})' " at line 12 (near
"filter: '({uid_key}={username})' ").

Answer 1

The problem is a vendor issue with symfony and is corrected already but not released as of this writing.
https://github.com/symfony/symfony/issues/39229

Answer 2

See: https://symfony.com/doc/current/components/yaml/yaml_format.html#strings
the part:
Strings containing any of the following characters must be quoted. Although you can use double quotes, for these characters it is more convenient to use single quotes, which avoids having to escape any backslash :
:, {, }, [, ], ,, &, *, #, ?, |, -, <, >, =, !, %, #, `
Can you try quoting all strings there? (using single quotes)
Also, which Symfony version?