Fix breakage due to reused type disappearing

[slevenick]

Fixes breakage in serialization.go preventing upgrade-dcl && make serialize from running. Should be no real downstream changes

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).
• [ ] Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• [ ] 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).
• [ ] Ran relevant acceptance tests (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)

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 3 files changed, 1238 insertions(+), 658 deletions(-)) Terraform Beta: Diff ( 3 files changed, 1277 insertions(+), 697 deletions(-)) TF Validator: Diff ( 2 files changed, 5 insertions(+), 5 deletions(-))

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDatasourceGoogleServiceNetworkingPeeredDnsDomain_basic|TestAccApigeeEnvironmentIamBindingGenerated|TestAccApigeeEnvironmentIamMemberGenerated|TestAccApigeeEnvironmentIamPolicyGenerated|TestAccCloudbuildWorkerPool_basic|TestAccComputeInstanceTemplate_reservationAffinities|TestAccContainerCluster_withAuthenticatorGroupsConfig|TestAccServiceNetworkingPeeredDNSDomain_basic You can view the result here: https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=259892

[modular-magician]

Tests failed during RECORDING mode: TestAccCloudbuildWorkerPool_basic|TestAccContainerCluster_withAuthenticatorGroupsConfig Please fix these to complete your PR