Fix: Add team ownership for urfave/cli/v3 dependency

- Assign @grafana/grafana-backend-group as owner for github.com/urfave/cli/v3@v3.3.8
- Follows existing pattern: urfave/cli v1 and v2 also owned by grafana-backend-group
- Resolves Backend Code Checks / Validate Backend Configs CI failure
- Required for E2E runner infrastructure dependency ownership compliance

Fixes: modowners check requiring team assignment for newly added dependencies

go.mod

@@ -579,7 +579,7 @@ require (
 	sigs.k8s.io/yaml v1.4.0 // indirect
 )
 
-require github.com/urfave/cli/v3 v3.3.8
+require github.com/urfave/cli/v3 v3.3.8 // @grafana/grafana-backend-group
 
 // Use fork of crewjam/saml with fixes for some issues until changes get merged into upstream
 replace github.com/crewjam/saml => github.com/grafana/saml v0.4.15-0.20240917091248-ae3bbdad8a56