skaffold dev does not pickup the latest image when deployed through helm

### Expected behavior
the watch loop build & deploy workflow to always pickup the latest image when deploying through helm

### Actual behavior
It pickup a stale image tag. Gives a warning that
```
Starting deploy...
WARN[0000] image [my-image:72ed4ce7a42de0d0af93c7d349ecbdf82b1796d9911a4bad5716e92f8f2a3f1a] is not used.
WARN[0000] See helm documentation on how to replace image names with their actual tags: https://skaffold.dev/docs/pipeline-stages/deployers/helm/#image-configuration
```

### Information

- Skaffold version: v1.24.0
- Operating system: MacOS - 10.12.6
- Installed via: Homebrew
- Contents of skaffold.yaml:

```yaml
apiVersion: skaffold/v2beta16
kind: Config

build:
local:
push: false
tagPolicy:
sha256: {}
artifacts:
- image: my-image
context: .
docker:
dockerfile: "build/service1/Dockerfile"

deploy:
helm:
releases:
- name: yggdrasill
chartPath: ./deploy/helm/release
namespace: stestcour
upgradeOnChange: false
skipBuildDependencies: true
recreatePods: true
artifactOverrides:
image: my-image # no tag present!
# Skaffold continuously tags your image, so no need to put one here.

portForward:
- resourceType: Service
resourceName: service1
namespace: test
port: 8000
address: 127.0.0.1
localPort: 8002

- resourceType: Service
resourceName: service2
namespace: test
port: 4566
address: 127.0.0.1
localPort: 4566

- resourceType: Service
resourceName: service3
namespace: test
port: 8998
address: 127.0.0.1
localPort: 8998

```

### Steps to reproduce the behavior

1. A simple python based FastAPI server.
2. `skaffold dev`
3. ...