Using secrets from GCP Secret Manager in Helm GCP Cloud Builder

## Affected builder image

`gcr.io/cloud-builders-community/helm`

## Expected Behavior
When I want to inject secret variables from GCP Secret Manager in helm step then injected values should have proper values which are hide under their names:

```
steps:
- name: gcr.io/$PROJECT_ID/helm
args:
- upgrade
- "$_NAME"
- "./deployment/charts/$_NAME"
- "--namespace"
- "$_NAMESPACE"
- "--set"
- "secret.var3=$$VAR3"
env:
- "CLOUDSDK_COMPUTE_ZONE=$_GKE_LOCATION"
- "CLOUDSDK_CONTAINER_CLUSTER=$_GKE_CLUSTER"
secretEnv: ['VAR3']
id: Apply deploy
substitutions:
_GKE_LOCATION: europe-west3-b
_GKE_CLUSTER: cluster-name
_NAME: "test"
_NAMESPACE: "test"
availableSecrets:
secretManager:
- versionName: projects/$PROJECT_ID/secrets/test-var-3/versions/latest
env: 'VAR3'
options:
substitution_option: 'ALLOW_LOOSE'
```

## Actual Behavior

Now injected value is equal to "$VAR3" not the value what is behind those name.

## Additional Info

According to documentation and [example in docker](https://cloud.google.com/build/docs/securing-builds/use-secrets#access-utf8-secrets) to inject values properly I can use "bash" entrypoint from the image but when I try do this with helm image as example below:

```
steps:
- name: gcr.io/$PROJECT_ID/helm
entrypoint: 'bash'
args:
- |
helm upgrade $_NAME ./deployment/charts/$_NAME --namespace $_NAMESPACE --set secret.var3="$$VAR3"
env:
- "CLOUDSDK_COMPUTE_ZONE=$_GKE_LOCATION"
- "CLOUDSDK_CONTAINER_CLUSTER=$_GKE_CLUSTER"
secretEnv: ['VAR3']
id: Apply deploy
substitutions:
_GKE_LOCATION: europe-west3-b
_GKE_CLUSTER: cluster-name
_NAME: "test"
_NAMESPACE: "test"
availableSecrets:
secretManager:
- versionName: projects/$PROJECT_ID/secrets/test-var-3/versions/latest
env: 'VAR3'
options:
substitution_option: 'ALLOW_LOOSE'
```
I got an error:

```
UPGRADE FAILED: Kubernetes cluster unreachable: Get "http://localhost:8080/version?timeout=32s": dial tcp 127.0.0.1:8080: connect: connection refused
```
which is understandable because helm first need to as I understand connect with cluster.

Is it possible inject some how values from secret manager properly in traditional way or use 'bash' option?