Update dependency ember-bootstrap to v6

Author: renovate[bot]

ember/package.json

@@ -42,7 +42,7 @@
     "broccoli-asset-rev": "3.0.0",
     "ember-ajax": "5.0.0",
     "ember-auto-import": "1.11.2",
-    "ember-bootstrap": "4.3.0",
+    "ember-bootstrap": "6.4.2",
     "ember-cli": "3.26.0",
     "ember-cli-babel": "7.26.6",
     "ember-cli-bundle-analyzer": "0.2.2",