Fix config for running FastBoot tests

It was intended before to run FastBoot tests only within the explicit ember-try scenario, but actually they did run for every scenario. This should fix it.

However we may revise that later, as FastBoot tests using `ember-cli-fastboot-testing` don't suffer from the overhead they had before. But we should do that eventually only after glimmerjs/glimmer-vm#1141 is fixed, which currently causes FastBoot tests to fail for Ember beta/canary.

config/ember-try.js

@@ -6,7 +6,7 @@ const bootstrapVersion = process.env.BOOTSTRAPVERSION === '3' ? '^3.4.1' : '^4.3
 module.exports = async function () {
   return {
     useYarn: true,
-    command: 'ember test --filter !FastBoot',
+    command: 'ember test --filter="\\!FastBoot"',
     scenarios: [
       {
         name: 'ember-lts-3.16',