extraVolumes block fails for alertmanager

[sem1993]

Describe the bug

Change from indent to nindent in alertmanager-dep.yaml template.

To Reproduce

Specify such block for alertmanager in values.yaml:

extraVolumes:
  - name: test-volume
     secret:
       secretName: test-secret

1. Start Mimir (SHA or version) - chart 5.5.1
2. Perform Operations(Read/Write/Others) - install

Expected behavior

A clear and concise description of what you expected to happen.
Clear installation without additional Helm chart tweaking.

Environment

• Infrastructure: [e.g., Kubernetes, bare-metal, laptop] - Kubernetes cluster v.1.29
• Deployment tool: [e.g., helm, jsonnet] - Helm