fix missing variable when building the image on cloudbuild

[cpanato]

What type of PR is this?
/kind bug

What this PR does / why we need it:
When we built the image k8s.gcr.io/cloud-provider-gcp/gcp-compute-persistent-disk-csi-driver:v1.2.1 we missed one parameter that needs to be set during the compilation process

This PR fix that, making it similar in how we build the image for windows.

built on my GCP account and now we can run the image without the error we saw before

$ docker run -it k8s.gcr.io/cloud-provider-gcp/gcp-compute-persistent-disk-csi-driver:v1.2.1
F0421 13:50:23.955027       1 main.go:71] version must be set at compile time

# after the fix
$ docker run -it gcr.io/cpanato-general/gcp-compute-persistent-disk-csi-driver:v99.99.99
W0421 13:50:31.576613       1 gce.go:137] GOOGLE_APPLICATION_CREDENTIALS env var not set
F0421 13:50:31.576650       1 main.go:103] Failed to get cloud provider: google: could not find default credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.

We will need to release a version v1.2.2 to fix the image issue

this PR is needed to unblock kubernetes/kubernetes#100747

/assign @msau42 @mattcary @saikat-royc

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Update base image to buster-1.6.0

[mattcary]

We should update this to buster 1.6.0 too.

[cpanato]

@mattcary done. ptal

I also build the image on my cloudbuild and works fine

[mattcary]

/lgtm

The presubmit is still not very healthy, we're working on it :-/

[mattcary]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, mattcary

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [mattcary]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment