Dedup gcp preconfigure check

[VenelinMartinov]

similar to pulumi/pulumi-aws#2949

Run preconfigure check only once. This removes duplication of config warnings.

Before:

Diagnostics:
  pulumi:pulumi:Stack (gcp_vm-dev):
    warning: unable to detect a global setting for GCP Project;
    Pulumi will rely on per-resource settings for this operation.
    Set the GCP Project by using:
        `pulumi config set gcp:project <project>`
    warning: unable to detect a global setting for GCP Project;
    Pulumi will rely on per-resource settings for this operation.
    Set the GCP Project by using:
        `pulumi config set gcp:project <project>`
    error: preview failed

After:

Diagnostics:
  pulumi:pulumi:Stack (gcp_vm-dev):
    warning: unable to detect a global setting for GCP Project;
    Pulumi will rely on per-resource settings for this operation.
    Set the GCP Project by using:
    	`pulumi config set gcp:project <project>`

[github-actions]

Does the PR have any schema changes?

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

Maintainer note: consult the runbook for dealing with any breaking changes.

[t0yv0]