backup/vault_policy: Improve diff handling for policies

[YakDriver]

Description

Relations

Relates #23288

References

Output from Acceptance Testing

% make testacc TESTS=TestAccBackupVaultPolicy_ PKG=backup
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/backup/... -v -count 1 -parallel 20 -run='TestAccBackupVaultPolicy_'  -timeout 180m
=== RUN   TestAccBackupVaultPolicy_basic
=== PAUSE TestAccBackupVaultPolicy_basic
=== RUN   TestAccBackupVaultPolicy_disappears
=== PAUSE TestAccBackupVaultPolicy_disappears
=== RUN   TestAccBackupVaultPolicy_Disappears_vault
=== PAUSE TestAccBackupVaultPolicy_Disappears_vault
=== RUN   TestAccBackupVaultPolicy_ignoreEquivalent
=== PAUSE TestAccBackupVaultPolicy_ignoreEquivalent
=== CONT  TestAccBackupVaultPolicy_basic
=== CONT  TestAccBackupVaultPolicy_Disappears_vault
=== CONT  TestAccBackupVaultPolicy_disappears
=== CONT  TestAccBackupVaultPolicy_ignoreEquivalent
--- PASS: TestAccBackupVaultPolicy_Disappears_vault (14.93s)
--- PASS: TestAccBackupVaultPolicy_disappears (17.28s)
--- PASS: TestAccBackupVaultPolicy_ignoreEquivalent (24.10s)
--- PASS: TestAccBackupVaultPolicy_basic (30.51s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/backup	35.154s

[github-actions]

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[github-actions]

This functionality has been released in v4.50.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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