fix drone build failure

`go install ginkgo` followed by `which ginkgo` is newly added in the upstream repo.
This is making the drone build fail for arm64 arch. The ginkgo library
gets installed under $GOPATH/bin/linux_arm64 dir. This is unlike amd64 images
which typically install go libraries under $GOPATH/bin. Since the previously mentioned
dir is not in PATH, the command `which ginkgo` fails. I've added this location to PATH
to fix the build failure. See upstream PRs linked below for more info:
kubernetes#8566
kubernetes#8569

build/run-in-docker.sh

@@ -89,6 +89,7 @@ if [[ "$DOCKER_IN_DOCKER_ENABLED" == "true" ]]; then
   #go env
   go install -mod=mod github.com/onsi/ginkgo/v2/ginkgo@v2.15.0
   find / -type f -name ginkgo 2>/dev/null
+  PATH=$PATH:$GOPATH/bin/linux_arm64
   which ginkgo
   /bin/bash -c "${FLAGS}"
 else