Automatic merge from submit-queue
Fix typo in test/images/port-forward-tester/Makefile
**What this PR does / why we need it**: the image build fails due to this typo:
```console
$ make WHAT=port-forward-tester
./image-util.sh build port-forward-tester
Building image for port-forward-tester ARCH: ppc64le...
make[1]: Entering directory '[home]/src/k8s.io/kubernetes/test/images/port-forward-tester'
../image-util.sh bin
../image-util.sh: line 22: $2: unbound variable
```
Images already pushed.
**Release note**:
```release-note
NONE
```
/approve no-issue
/assign @mkumatag
44b0e1080d