chore: make run-against-dist permanently install Verdaccio tool

We can't combine `--daemon` with running ephemerally using `npx`,
or the directory will be removed too quickly.

Fixes the build.

packages/aws-cdk/test/integ/run-against-dist.bash

@@ -70,6 +70,10 @@ function serve_npm_packages() {
   # Start a mock npm repository from the given tarballs
   #------------------------------------------------------------------------------
   header "Starting local NPM Repository"
+
+  # When using '--daemon', 'npm install' first so the files are permanent, or
+  # 'npx' will remove them too soon.
+  npm install serve-npm-tarballs
   eval $(npx serve-npm-tarballs --glob "${tarballs_glob}" --daemon)
   trap "kill $SERVE_NPM_TARBALLS_PID" EXIT
 }