Reproduction Steps
I created a simple bundle with the configuration of the Health advisor plugin in the Jenkins.yaml file like described in the documentation :

jenkins:
  systemMessage: "Controller configured using CloudBees CasC"c
  numExecutors: 0
advisor:
  acceptToS: true
  email: "${admin_mail}"  
  excludedComponents:
  - "AgentsSystemConfiguration"
  - "AgentsJVMProcessSystemMetricsContents"
  nagDisabled: false

Also, we have a variables.yaml file with the variable admin_mail defined:

variables:

    - team_name: Team Alpha
    - team_group: alpha
    - admin_mail: newmail@mail.com

Then I deployed a controller using that casc-bundle and when it starts I can see in Manage Jenkins-> Configure Jenkins Health Advisor by CloudBees I can see that the variable is not substituted for its value, as shown in the screenshot:

Additionally, if a `${variable}` is used in one of the CC: fields, it will not be correctly escaped when exported to yaml