FIX: Add missing Target Key

[djsd123]

Description

Add missing target key Functions to relevant validate function

See docs

Relations

Closes #41208

References

Output from Acceptance Testing

make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.23.5 test ./internal/service/fis/... -v -count 1 -parallel 20 -run='TestAccFISExperimentTemplate_basic'  -timeout 360m -vet=off
2025/02/03 18:04:40 Initializing Terraform AWS Provider...
=== RUN   TestAccFISExperimentTemplate_basic
=== PAUSE TestAccFISExperimentTemplate_basic
=== CONT  TestAccFISExperimentTemplate_basic
--- PASS: TestAccFISExperimentTemplate_basic (23.80s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/fis        26.916s

% make testacc TESTS=TestAccXXX PKG=ec2

...

[github-actions]

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