fmt: fix allocation tests
fmt: fix allocation tests

Converting an integer to an interface{} allocates as of CL 130240043.

Fixes issue 8617.

LGTM=r
R=r
CC=golang-codereviews, khr
https://codereview.appspot.com/141700043

wesolows/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old