[terraform-provider-octopusdeploy] octopusdeploy_tag create panics (nil pointer) when tag set update rejected

## Observed symptom `octopusdeploy_tag` create panics (nil pointer) when the tag set update is rejected, hiding the server's error When the server rejects the tag set update during `octopusdeploy_tag` create, the provider crashes instead of reporting the server's error. For example, a target tag whose name already exists in another Target-scoped tag set returns HTTP 400: "The following tag names already exist in other Target tag sets". **Cause (from reading the v1.20.0 source)** ## Literal error text ``` octopusdeploy_tag create panics nil pointer ``` ## Environment GitHub OctopusDeploy/terraform-provider-octopusdeploy #305 ## Trigger / context Public GitHub report in OctopusDeploy/terraform-provider-octopusdeploy (FRESH_7D). ## Source evidence - https://github.com/OctopusDeploy/terraform-provider-octopusdeploy/issues/305 (2026-09-30T19:06:23Z) — evidence_class: PRIMARY_ISSUE_REPORT — #305 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:49:02.645589Z - scout_id: C4674f755ca ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.