fix: change the type from array to slice to prevent a panic

[suzuki-shunsuke]

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Closes #22312.

Output from acceptance testing:

$ make testacc TESTS=TestAccEC2TrafficMirrorFilterRule PKG=ec2
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/ec2/... -v -count 1 -parallel 20 -run='TestAccEC2TrafficMirrorFilterRule' -timeout 180m
=== RUN   TestAccEC2TrafficMirrorFilterRule_basic
=== PAUSE TestAccEC2TrafficMirrorFilterRule_basic
=== RUN   TestAccEC2TrafficMirrorFilterRule_disappears
=== PAUSE TestAccEC2TrafficMirrorFilterRule_disappears
=== CONT  TestAccEC2TrafficMirrorFilterRule_basic
=== CONT  TestAccEC2TrafficMirrorFilterRule_disappears
--- PASS: TestAccEC2TrafficMirrorFilterRule_disappears (52.83s)
--- PASS: TestAccEC2TrafficMirrorFilterRule_basic (141.59s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/ec2	143.856s

[ewbankkit]

LGTM 🚀.

% make testacc PKG=ec2 TESTS=TestAccEC2TrafficMirrorFilterRule_basic
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/ec2/... -v -count 1 -parallel 20 -run='TestAccEC2TrafficMirrorFilterRule_basic' -timeout 180m
=== RUN   TestAccEC2TrafficMirrorFilterRule_basic
=== PAUSE TestAccEC2TrafficMirrorFilterRule_basic
=== CONT  TestAccEC2TrafficMirrorFilterRule_basic
--- PASS: TestAccEC2TrafficMirrorFilterRule_basic (45.75s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/ec2	52.453s

[ewbankkit]

@suzuki-shunsuke Thanks for the contribution 🎉 👏.

[github-actions]

This functionality has been released in v3.71.0 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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