Scene "Export As..." menu item disabled in master

[aaronfranke]

Tested versions

Reproducible in commit f00cf63 (PR #107652)
Not reproducible in commit 359ef8f (the previous commit)

System information

macOS Sequoia 15.7

Issue description

As of PR #107652, the "Export As..." button is grayed out:

Steps to reproduce

Have a Godot project open with a scene open, click "Scene" in the menu bar, and try to click "Export As..."

Minimal reproduction project (MRP)

N/A