Revert "Revert "Merge branch 'master' of https://github.com/discourse/discourse""

This reverts commit 20780a1eeed56b321daf18ee6bbfe681a51d1bf4.

* SECURITY: re-adds accidentally reverted commit:
  03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
  instead of the 03d26cd6 parent (which contains security fixes)

spec/requests/admin/backups_controller_spec.rb

@@ -35,7 +35,7 @@ RSpec.describe Admin::BackupsController do
   end
 
   after do
-    Discourse.redis.flushall
+    Discourse.redis.flushdb
 
     @paths&.each { |path| File.delete(path) if File.exists?(path) }
     @paths = nil