Add cflinuxfs5 to install_go.sh stack allowlist

When deploying via git URL, CF runs bin/supply as a shell script which
sources scripts/install_go.sh to bootstrap Go compilation. The stack
check only allowed cflinuxfs3 and cflinuxfs4, causing cflinuxfs5
deployments to fail with 'Unsupported stack' before any Go code runs.

The Go binary (cflinuxfs3) is forward-compatible and works on all
three stacks.

Author: tnikolova82

scripts/install_go.sh

@@ -5,7 +5,7 @@ set -u
 set -o pipefail
 
 function main() {
-  if [[ "${CF_STACK:-}" != "cflinuxfs3" && "${CF_STACK:-}" != "cflinuxfs4" ]]; then
+  if [[ "${CF_STACK:-}" != "cflinuxfs3" && "${CF_STACK:-}" != "cflinuxfs4" && "${CF_STACK:-}" != "cflinuxfs5" ]]; then
     echo "       **ERROR** Unsupported stack"
     echo "                 See https://docs.cloudfoundry.org/devguide/deploy-apps/stacks.html for more info"
     exit 1