Fixes aws_lb_listener datasource's default_action's target_group_arn

[tmarlok88]

Fixes #36459 where the default_action's target_group_arn is not filled in an aws_lb_listener datasource

Description

The default_action.target_group_arn attribute in an aws_lb_listener data source is empty.

Relations

Closes #36459

References

The bug was introduced in this PR: #35671

Output from Acceptance Testing

$ make testacc TESTARGS='-run=TestAccELBV2ListenerDataSource_basic' PKG=elbv2 ACCTEST_PARALLELISM=2 
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.22.2 test ./internal/service/elbv2/... -v -count 1 -parallel 2  -run=TestAccELBV2ListenerDataSource_basic -timeout 360m
=== RUN   TestAccELBV2ListenerDataSource_basic
=== PAUSE TestAccELBV2ListenerDataSource_basic
=== CONT  TestAccELBV2ListenerDataSource_basic
--- PASS: TestAccELBV2ListenerDataSource_basic (228.43s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/elbv2	228.617s

...

[github-actions]

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[tmarlok88]

@gdavison This fix messes with your recent PR (mentioned in the description), please give some sanity check if you have the time.