Bug Fix azuredevops_build_folder - Fix build folder import bug

[xuzhang3]

All Submissions:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code follows the code style of this project.
• I ran lint checks locally prior to submission.
• Have you checked to ensure there aren't other open PRs for the same update/change?

What about the current behavior has changed?

Issue Number: #1137
Fix build folder import bug and update test case

=== RUN   TestAccBuildFolder_basic
=== PAUSE TestAccBuildFolder_basic
=== RUN   TestAccBuildFolder_update
=== PAUSE TestAccBuildFolder_update
=== RUN   TestAccBuildFolder_requiresImportErrorStep
=== PAUSE TestAccBuildFolder_requiresImportErrorStep
=== CONT  TestAccBuildFolder_basic
=== CONT  TestAccBuildFolder_requiresImportErrorStep
=== CONT  TestAccBuildFolder_update
--- PASS: TestAccBuildFolder_basic (73.25s)
--- PASS: TestAccBuildFolder_requiresImportErrorStep (83.56s)
--- PASS: TestAccBuildFolder_update (113.58s)
PASS
ok      github.com/microsoft/terraform-provider-azuredevops/azuredevops/internal/acceptancetests        118.807s

Does this introduce a change to go.mod, go.sum or vendor/?

• Yes
• No

Does this introduce a breaking change?

• Yes
• No

Any relevant logs, error output, etc?

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