fix: notifications processing crash for task triggered pipelines

[hamir-suspect]

📝 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

• I have tested this change
• This change requires documentation update