fix: notifications processing crash for task triggered pipelines (#601)

## 📝 Description
For task runs there is no hook -> failed processing of pipeline finished
message, this fixes the issue and takes if possible tag and pr names
from hook, otherwise falls back to pipeline data.

#### `logs`
```
INFO 2025-09-22T15:18:44.605829774Z [resource.labels.containerName: notifications] ** (UndefinedFunctionError) function nil.git_ref_type/0 is undefined
INFO 2025-09-22T15:18:44.605831724Z [resource.labels.containerName: notifications] nil.git_ref_type()
INFO 2025-09-22T15:18:44.605834104Z [resource.labels.containerName: notifications] (notifications 0.1.0) lib/notifications/workers/coordinator.ex:29: anonymous fn/1 in Notifications.Workers.Coordinator.PipelineFinished.handle_message/1
```
this issue was present before
#591 was merged also:
```
INFO 2025-09-22T12:33:05.523589599Z [resource.labels.containerName: notifications] ** (UndefinedFunctionError) function nil.pr_branch_name/0 is undefined
INFO 2025-09-22T12:33:15.596608567Z [resource.labels.containerName: notifications] ** (UndefinedFunctionError) function nil.pr_branch_name/0 is undefined
INFO 2025-09-22T12:33:25.758473405Z [resource.labels.containerName: notifications] ** (UndefinedFunctionError) function nil.pr_branch_name/0 is undefined
```
## ✅ Checklist
- [x] I have tested this change
- [ ] This change requires documentation update

Author: hamir-suspect

notifications/lib/notifications/workers/coordinator.ex

@@ -26,9 +26,7 @@ defmodule Notifications.Workers.Coordinator do
 
         Logger.info("#{request_id} #{event.pipeline_id} #{project.metadata.name}")
 
-        tag_name = if hook.git_ref_type == :TAG, do: hook.tag_name, else: nil
-        branch_name = if hook.git_ref_type == :TAG, do: nil, else: pipeline.branch_name
-        pr_branch_name = if hook.git_ref_type == :TAG, do: "", else: hook.pr_branch_name
+        {tag_name, branch_name, pr_branch_name} = extract_references(pipeline, hook)
 
         rules =
           Filter.find_rules(
@@ -103,6 +101,15 @@ defmodule Notifications.Workers.Coordinator do
       end
     end
 
+    defp extract_references(pipeline, nil), do: extract_references_from_pipeline(pipeline)
+    defp extract_references(_pipeline, hook = %{git_ref_type: :TAG}), do: {hook.tag_name, nil, ""}
+    defp extract_references(pipeline, hook), do: {nil, pipeline.branch_name, hook.pr_branch_name}
+
+    defp extract_references_from_pipeline(%{branch_name: "refs/tags" <> tag_name}),
+      do: {tag_name, nil, ""}
+
+    defp extract_references_from_pipeline(%{branch_name: branch_name}), do: {nil, branch_name, ""}
+
     defp map_result_to_string(enum), do: enum |> Atom.to_string() |> String.downcase()
   end
 end