Error when recreating PagerDuty workflow

output.txt

```
Stack trace from the terraform-provider-pagerduty_v3.17.0 plugin:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xe84165]

goroutine 85 [running]:
github.com/PagerDuty/terraform-provider-pagerduty/pagerduty.flattenIncidentWorkflowTrigger(0xc000012398?, 0xc0004374a0)
github.com/PagerDuty/terraform-provider-pagerduty/pagerduty/resource_pagerduty_incident_workflow_trigger.go:212 +0x85
github.com/PagerDuty/terraform-provider-pagerduty/pagerduty.fetchIncidentWorkflowTrigger.func1()
github.com/PagerDuty/terraform-provider-pagerduty/pagerduty/resource_pagerduty_incident_workflow_trigger.go:202 +0x25b
github.com/hashicorp/terraform-plugin-sdk/v2/helper/retry.RetryContext.func1()
github.com/hashicorp/terraform-plugin-sdk/[email protected]/helper/retry/wait.go:30 +0x56
github.com/hashicorp/terraform-plugin-sdk/v2/helper/retry.(*StateChangeConf).WaitForStateContext.func1()
github.com/hashicorp/terraform-plugin-sdk/[email protected]/helper/retry/state.go:113 +0x1c4
created by github.com/hashicorp/terraform-plugin-sdk/v2/helper/retry.(*StateChangeConf).WaitForStateContext
github.com/hashicorp/terraform-plugin-sdk/[email protected]/helper/retry/state.go:86 +0x1d8

Error: The terraform-provider-pagerduty_v3.17.0 plugin crashed!

This is always indicative of a bug within the plugin. It would be immensely
helpful if you could report the crash with the plugin's maintainers so that it
can be fixed. The output above should help diagnose the issue.
```