[Bug]: Runpod: pod won't start if `registry_auth` is specified

[un-def]

Steps to reproduce

type: task
image: registry.example.com/ns/repo:tag
registry_auth:
  username: ${{ secrets.REGISTRY_USERNAME }}
  password: ${{ secrets.REGISTRY_PASSWORD }}

dstack apply --backend runpod

Actual behaviour

The run gets stuck in provisioning

Pod logs (the same messages repeated over and over again):

create container registry.example.com/ns/repo:tag
tag Pulling from registry.example.com/ns/repo
Digest: sha256:a3d14abd7cc33008f7a690afdf7a76da90d943a68a9676dbf6fd2c696fb15d20
Status: Image is up to date for registry.example.com/ns/repo:tag
error creating container: container: create: container create: Error response from daemon: invalid mount config for type "bind": field Target must not be empty

Expected behaviour

No response

dstack version

0.20.19

Server logs

Additional information

A pod is created without a so-called Pod volume (a local volume attached to the pod container; survives pod restarts) (volumeInGb: 0):

dstack/src/dstack/_internal/core/backends/runpod/api_client.py

Line 61 in 9e23658

volume_in_gb: int = 0,

But when it's updated to include registry creds, the Pod volume is specified (volumeInGb: 20):

dstack/src/dstack/_internal/core/backends/runpod/api_client.py

Lines 151 to 153 in 9e23658

	# Default pod volume is 20GB.
	# Runpod errors if it's not specified for podEditJob.
	volume_in_gb: int = 20,

Apparentry, Runpod tries to restart the pod with a volume attached (a bind mount), but there is no volume created, thus field Target must not be empty