actions-runner-controller: v0.20 Problem with authentication on controller-manager

Describe the bug It seems that controller-manager deployment from yaml is not using environment variables correctly.

Checks

• My actions-runner-controller version (v0.x.y) does support the feature
• I’m using an unreleased version of the controller I built from HEAD of the default branch

To Reproduce Steps to reproduce the behavior:

1. deploy actions-runner-controller v0.20.0 from release page
2. deploy secret with github app key and ids
3. Try deploying any runner
4. Get error in controller-manager saying that key file has length 0

Expected behavior Github runner should be registered

Environment (please complete the following information):

• Controller Version: 0.20.0
• Deployment Method: kubectl apply

Additional context I have created a workaround by manually providing required arguments to /manager binary, see below:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    control-plane: controller-manager
  name: controller-manager
  namespace: actions-runner-system
spec:
  replicas: 1
  selector:
    matchLabels:
      control-plane: controller-manager
  template:
    metadata:
      labels:
        control-plane: controller-manager
    spec:
      containers:
      - name: manager
        command:
        - "/manager" 
        args:
        - --metrics-addr=127.0.0.1:8080
        - --enable-leader-election
        - --sync-period=10m
        - "-github-app-private-key" 
        - $(GITHUB_APP_PRIVATE_KEY)
        - "-github-app-id"
        - $(GITHUB_APP_ID)
        - "-github-app-installation-id"
        - $(GITHUB_APP_INSTALLATION_ID)
        env:
        - name: GITHUB_TOKEN
          valueFrom:
            secretKeyRef:
              key: github_token
              name: controller-manager
              optional: true
        - name: GITHUB_APP_ID
          valueFrom:
            secretKeyRef:
              key: github_app_id
              name: controller-manager
              optional: true
        - name: GITHUB_APP_INSTALLATION_ID
          valueFrom:
            secretKeyRef:
              key: github_app_installation_id
              name: controller-manager
              optional: true
        - name: GITHUB_APP_PRIVATE_KEY
          value: /etc/actions-runner-controller/github_app_private_key
        image: summerwind/actions-runner-controller:v0.20.0
        ports:
        - containerPort: 9443
          name: webhook-server
          protocol: TCP
        resources:
          limits:
            cpu: 100m
            memory: 100Mi
          requests:
            cpu: 100m
            memory: 20Mi
        volumeMounts:
        - mountPath: /tmp/k8s-webhook-server/serving-certs
          name: cert
          readOnly: true
        - mountPath: /etc/actions-runner-controller
          name: controller-manager
          readOnly: true
      - args:
        - --secure-listen-address=0.0.0.0:8443
        - --upstream=http://127.0.0.1:8080/
        - --logtostderr=true
        - --v=10
        image: quay.io/brancz/kube-rbac-proxy:v0.10.0
        name: kube-rbac-proxy
        ports:
        - containerPort: 8443
          name: https
      terminationGracePeriodSeconds: 10
      volumes:
      - name: cert
        secret:
          defaultMode: 420
          secretName: webhook-server-cert
      - name: controller-manager
        secret:
          secretName: controller-manager
---