Don't lock policy if it is already locked.

[nat-henderson]

Release Note Template for Downstream PRs (will be copied)

`storage`: Fixed error in `google_storage_bucket` where locked retention policies would cause a bucket to report failure on all updates (even though updates were applied correctly).

Fixes hashicorp/terraform-provider-google#4751

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, c74805c.

Pull request statuses

WARNING: The following files changed in commit c74805c may need corresponding changes in third_party/validator:

• third_party/terraform/resources/resource_storage_bucket.go

No diff detected in terraform-google-conversion.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#1307
depends: hashicorp/terraform-provider-google#4761

[megan07]

LGTM!

[megan07]

Oh! I would double check this release note as well. To start with storage: and the past tense Fixed I think