Regression: Closing a second window also closes the first

[jeremypw]

What Happened?

Opened a second window and then closed it from the headerbar. Both windows closed

Steps to Reproduce

1. Open two Code windows
2. Close the second
3. The first also closes

Expected Behavior

Only the second window closes, similar to apps like Files and Terminal

OS Version

8.x (Circe)

Session Type

Secure Session (Wayland)

Software Version

Latest release (I have run all updates)

Log Output

Gdb indicates the app closed normally.

Hardware Info

No response