Backend/COS: remove COS object lock tag either when unlock remote state

[Kagashino]

When running command terraform force-unlock , the remote state file will be removed as expect. However, the tencentcloud-terraform-lock tag will not removed at the same time in some unexpected program exit cases. Creating this PR is purpose to ensure the tag removed to get rid of impact of next terraform operation.

Here shows the unit test output:

$ TF_ACC=1 go test -v ./internal/backend/remote-state/cos

=== RUN   TestStateFile
=== PAUSE TestStateFile
=== RUN   TestRemoteClient
=== PAUSE TestRemoteClient
=== RUN   TestRemoteClientWithPrefix
=== PAUSE TestRemoteClientWithPrefix
=== RUN   TestRemoteClientWithEncryption
=== PAUSE TestRemoteClientWithEncryption
=== RUN   TestRemoteLocks
=== PAUSE TestRemoteLocks
=== RUN   TestBackend
=== PAUSE TestBackend
=== RUN   TestBackendWithPrefix
=== PAUSE TestBackendWithPrefix
=== RUN   TestBackendWithEncryption
=== PAUSE TestBackendWithEncryption
=== CONT  TestBackendWithPrefix
=== CONT  TestStateFile
=== RUN   TestStateFile/_default.tfstate_default
=== CONT  TestBackend
=== RUN   TestStateFile/_test.tfstate_default
=== RUN   TestStateFile/_test.tfstate_dev
=== RUN   TestStateFile/terraform/test_default.tfstate_default
=== CONT  TestRemoteLocks
=== CONT  TestRemoteClientWithEncryption
=== CONT  TestRemoteClientWithPrefix
=== CONT  TestRemoteClient
=== CONT  TestBackendWithEncryption
=== CONT  TestBackend
=== CONT  TestBackendWithPrefix
=== CONT  TestRemoteClientWithPrefix
=== CONT  TestBackendWithEncryption
=== CONT  TestRemoteClient
=== RUN   TestStateFile/terraform/test_test.tfstate_default
=== CONT  TestRemoteClientWithEncryption
=== CONT  TestRemoteLocks
=== RUN   TestStateFile/terraform/test_test.tfstate_dev
--- PASS: TestStateFile (0.00s)
    --- PASS: TestStateFile/_default.tfstate_default (0.00s)
    --- PASS: TestStateFile/_test.tfstate_default (0.00s)
    --- PASS: TestStateFile/_test.tfstate_dev (0.00s)
    --- PASS: TestStateFile/terraform/test_default.tfstate_default (0.00s)
    --- PASS: TestStateFile/terraform/test_test.tfstate_default (0.00s)
    --- PASS: TestStateFile/terraform/test_test.tfstate_dev (0.00s)
=== CONT  TestBackendWithPrefix
=== CONT  TestBackendWithEncryption
=== CONT  TestBackend
--- PASS: TestRemoteClientWithPrefix (1.79s)
--- PASS: TestRemoteClientWithEncryption (1.84s)
--- PASS: TestRemoteClient (1.90s)
--- PASS: TestRemoteLocks (3.25s)
=== CONT  TestBackend
=== CONT  TestBackendWithEncryption
=== CONT  TestBackendWithPrefix
=== CONT  TestBackend
    testing.go:300: TestBackend: testing state locking for *cos.Backend
=== CONT  TestBackendWithEncryption
    testing.go:300: TestBackend: testing state locking for *cos.Backend
=== CONT  TestBackendWithPrefix
    testing.go:300: TestBackend: testing state locking for *cos.Backend
=== CONT  TestBackend
    testing.go:300: TestBackend: testing state locking for *cos.Backend
--- PASS: TestBackendWithEncryption (6.95s)
--- PASS: TestBackendWithPrefix (7.01s)
--- PASS: TestBackend (9.15s)
PASS
ok      github.com/hashicorp/terraform/internal/backend/remote-state/cos        9.532s

[crw]

Thanks for this submission! Just a note that there is a general hold on backend reviews (see CONTRIBUTING.md#state-storage-backends. I will update this PR if/when that is lifted.

I see that @likexian is listed as the maintainer of this backend in CODEOWNERS. We would need a review from @likexian before moving forward. However, given the above hold on reviews, we cannot guarantee the core team will be able to review it in the near future.

Thanks again for your submission!

[likexian]

Hello @crw
LGTM

[jbardin]

Thanks @likexian!

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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