iot/policy: Fix diffs with equivalent policies

[YakDriver]

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Relates #21968

Output from acceptance testing:

% make testacc TESTS=TestAccIoTPolicy_basic PKG=iot
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/iot/... -v -count 1 -parallel 20 -run='TestAccIoTPolicy_basic' -timeout 180m
--- PASS: TestAccIoTPolicy_basic (16.54s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/iot	18.453s

[ewbankkit]

LGTM 🚀.

% make testacc TESTS=TestAccIoTPolicy_ PKG=iot     
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/iot/... -v -count 1 -parallel 20 -run='TestAccIoTPolicy_' -timeout 180m
=== RUN   TestAccIoTPolicy_basic
=== PAUSE TestAccIoTPolicy_basic
=== RUN   TestAccIoTPolicy_disappears
=== PAUSE TestAccIoTPolicy_disappears
=== CONT  TestAccIoTPolicy_basic
=== CONT  TestAccIoTPolicy_disappears
--- PASS: TestAccIoTPolicy_disappears (13.79s)
--- PASS: TestAccIoTPolicy_basic (17.25s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/iot	20.922s

[github-actions]

This functionality has been released in v3.70.0 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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