Fix inconsistent final plan when labels are added to resources

[modular-magician]

Users reported an issue creating buckets with labels via google_storage_bucket since #6518 was merged. Creation failed with the following error message:

Error: Provider produced inconsistent final plan

When expanding the plan for google_storage_bucket.test_bucket to include new values learned so far during apply, provider
"registry.terraform.io/hashicorp/google" produced an invalid new value for .labels: was null, but now
cty.MapVal(map[string]cty.Value{"one":cty.StringVal("bla"), "two":cty.StringVal("qny")}).

This is a bug in the provider, which should be reported in the provider's own issue tracker.

I am by far no Terraform expert but i looked at the other resources which had a DiffSuppressFunc set on their labels property and all of them had computed: true EXCEPT google_dataflow_job. So i ran a small test with

resource "google_dataflow_job" "big_data_job" {
  name              = "dataflow-job"
  template_gcs_path = "gs://my-bucket/templates/template_file"
  temp_gcs_location = "gs://my-bucket/tmp_dir"
  parameters = {
    foo = "bar"
    baz = "qux"
  }
  labels = {
    for = "bar"
  }
}

and it seems that this resource has the same problem as google_storage_bucket:

Error: Provider produced inconsistent final plan
 
When expanding the plan for google_dataflow_job.big_data_job to include new values learned so far during apply, provider
"registry.terraform.io/hashicorp/google" produced an invalid new value for .labels: was null, but now
cty.MapVal(map[string]cty.Value{"one":cty.StringVal("foo"), "two":cty.StringVal("bar")}).

This is a bug in the provider, which should be reported in the provider's own issue tracker.

Setting both properties to computed: true in alignment with the others fixed the problem on both resources. But please don't ask me why 😁

@prauc FYI

Fixes #12804

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

storage: fixed inconsistent final plan when labels are added to `google_storage_bucket`

dataflow: fixed inconsistent final plan when labels are added to `google_dataflow_job`

Derived from GoogleCloudPlatform/magic-modules#7923

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