Add calls to t.Helper() in defered functions

[ewbankkit]

Adds missing calls to t.Helper() in two defered functions.

Closes #292.

% go test ./...
?   	github.com/hashicorp/terraform-plugin-testing/helper/logging	[no test files]
ok  	github.com/hashicorp/terraform-plugin-testing/config	2.009s
ok  	github.com/hashicorp/terraform-plugin-testing/helper/acctest	2.362s
?   	github.com/hashicorp/terraform-plugin-testing/internal/addrs	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testprovider	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testsdk	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testsdk/datasource	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testsdk/provider	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testsdk/providerserver	[no test files]
?   	github.com/hashicorp/terraform-plugin-testing/internal/testing/testsdk/resource	[no test files]
ok  	github.com/hashicorp/terraform-plugin-testing/helper/resource	95.516s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/configs/configschema	0.644s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/configs/hcl2shim	2.394s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/logging	0.924s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/plugintest	10.395s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/teststep	1.521s
ok  	github.com/hashicorp/terraform-plugin-testing/internal/tfdiags	1.910s
ok  	github.com/hashicorp/terraform-plugin-testing/knownvalue	2.024s
ok  	github.com/hashicorp/terraform-plugin-testing/plancheck	8.467s
ok  	github.com/hashicorp/terraform-plugin-testing/statecheck	5.476s
ok  	github.com/hashicorp/terraform-plugin-testing/terraform	4.563s
ok  	github.com/hashicorp/terraform-plugin-testing/tfjsonpath	4.606s
ok  	github.com/hashicorp/terraform-plugin-testing/tfversion	129.643s

[austinvalle]

LGTM 🚀 - I pushed a small changelog for the fix, thanks @ewbankkit

[github-actions]

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