Fix pause_mode may not be converted correctly in .tscn files.

[Maran23]

Fixes: #74845

A pause_mode of 2 was not converted correctly.
In Godot 3, the pause_mode of 2 equals the PAUSE_MODE_PROCESS value.
In Godot 4, the pause_mode PAUSE_MODE_PROCESS was renamed to PROCESS_MODE_ALWAYS and equals the number 3.

The fix is therefore to convert the pause_mode = 2 to pause_mode = 3 (PAUSE_MODE_PROCESS -> PROCESS_MODE_ALWAYS) in .tscn files.

[akien-mga]

Thanks!