all: format sources with gofumpt v0.9.1

Since gofumpt v0.9.0 there's a new formatting rule to "clothe" any naked
returns.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/utils/utils.go

@@ -112,5 +112,5 @@ func Annotations(labels []string) (bundle string, userAnnotations map[string]str
 			userAnnotations[name] = value
 		}
 	}
-	return
+	return bundle, userAnnotations
 }