Pass through GOCACHE to test_env

Otherwise the cache gets written to bundles instead of to the volume
that we setup in the Makefile as expected.

Found this because vscode did not like having these huge objects in
bundles/ (didn't harm anything, just that it noticed and said hey I don't
like that).

This enables cache-reuse when building the test binaries.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

hack/make/.integration-test-helpers

@@ -16,6 +16,7 @@ source "${MAKEDIR}/.go-autogen"
 : "${TEST_REPEAT:=1}"
 : "${TESTFLAGS:=}"
 : "${TESTDEBUG:=}"
+: "${GOCACHE:=$(go env GOCACHE)}"
 
 setup_integration_test_filter() {
 	if [ -z "${TEST_FILTER}" ]; then
@@ -149,6 +150,7 @@ test_env() {
 			DOCKER_REMOTE_DAEMON="$DOCKER_REMOTE_DAEMON" \
 			DOCKER_ROOTLESS="$DOCKER_ROOTLESS" \
 			DOCKERFILE="$DOCKERFILE" \
+			GOCACHE="$GOCACHE" \
 			GOPATH="$GOPATH" \
 			GOTRACEBACK=all \
 			HOME="$ABS_DEST/fake-HOME" \