Provide better npm options

* Use `--no-package-lock` (prevents a warning around using
  `--ignore-shrinkwrap`)
* Use `--legacy-peer-deps` to work around an issue with
  `@ember/test-helpers` having a peerDep on ember-source >= 3.8, but
  release/beta/canary channel downloads don't satisfy (in
  `semver.satisfies` terms)

test-app/config/ember-try.js

@@ -38,6 +38,10 @@ const embroider = {
 
 module.exports = async function() {
   return {
+    buildManagerOptions() {
+      return ['--no-package-lock', '--legacy-peer-deps'];
+    },
+
     scenarios: [
       {
         name: 'ember-lts-3.24',