Fix keep-failed-containers flag handling in integration script

The --keep-failed-containers flag was being passed as --keep-failed-containers=true/false
which doesn't work with Go's BoolVar flag parser. Boolean flags in Go expect
just --keep-failed-containers (for true) or nothing (for false).

Modified the script to only pass the flag when keep_failed is true, matching
Go's boolean flag expectations.

Author: ramonskie

scripts/integration.sh

@@ -125,14 +125,18 @@ function specs::run() {
   platform_flag="--platform=${platform}"
   stack_flag="--stack=${stack}"
   token_flag="--github-token=${token}"
-  keep_failed_flag="--keep-failed-containers=${keep_failed}"
+  keep_failed_flag=""
   nodes=1
 
   if [[ "${parallel}" == "true" ]]; then
     nodes=3
     serial_flag=""
   fi
 
+  if [[ "${keep_failed}" == "true" ]]; then
+    keep_failed_flag="--keep-failed-containers"
+  fi
+
   local buildpack_file version
   version="$(cat "${ROOTDIR}/VERSION")"
   buildpack_file="$(buildpack::package "${version}" "${cached}" "${stack}")"