We want to add the following snippet before inheriting from an immutable YAML that does the build job.

jobs:
  - job: PreBuild
    timeoutInMinutes: 120
    pool:
      name: 'poolname'
      vmImage: 'windows'
      steps:
        - checkout: self
          clean: true
          persistCredentials: true
        - task: ..........
          ......
        - task: ..........
          ......

But when we add the snippet before the extends, the YAML would prompt: Unexpected value 'extends'

extends:
  template: template.yml@TemplateRepo

So what is the best solution based on the immutable build templates to have us run several tasks before inheriting the template where template jobs always execute first?
Or, are there any other approaches that we could have everything inheriting inside the template but have our custom steps run first?