Fix bug: diff being detected for source_repo_repository even when there are no changes

[jcanseco]

This patch fixes a bug in source_repo_repository where a diff was always being generated for the TypeSet field pubsub_configs since its Set hashing function was not accounting for the fact that pubsub_configs[].topic can contain either a topic's name or relative path.

To reproduce, apply the following Terraform configuration, then run terraform plan right after. Notice how terraform plan detects a diff even when nothing was actually changed.

provider "google" {
  project = "my-project-test"
}

resource "google_pubsub_topic" "topic" {
  name = "my-topic-test"
}

resource "google_sourcerepo_repository" "repo" {
  name             = "my-repo-test"
  pubsub_configs {
    topic           = google_pubsub_topic.topic.name
    message_format  = "JSON"
  }
}

Release Note Template for Downstream PRs (will be copied)

sourcerepo: fixed perma-diff in `google_sourcerepo_repository`

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

Thanks for your contribution! A human will be with you soon.

@danawillow, please review this PR or find an appropriate assignee.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 20 insertions(+))
Terraform Beta: Diff ( 1 file changed, 20 insertions(+))
TF Conversion: Diff ( 1 file changed, 20 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=135982"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccFolderIamAuditConfig_multiple You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=135989"

[danawillow]

Thanks Jazel!