fix(docs): incorrect formatting trigger example (#566)

I noticed that the [current
docs](https://registry.terraform.io/providers/honeycombio/honeycombio/latest/docs/resources/trigger#example-with-pagerduty-recipient-and-severity)
have a malformed second example for Triggers.

This properly tags the code block as HCL which fixes the issue. You can
test yourself by copying and pasting the full file into the HashiCorp
[Doc Preview Tool](https://registry.terraform.io/tools/doc-preview)

docs/resources/trigger.md

@@ -55,7 +55,7 @@ resource "honeycombio_trigger" "example" {
 ```
 
 ### Example with PagerDuty Recipient and Severity
-```
+```hcl
 variable "dataset" {
   type = string
 }