AudioStream's "_instantiate_playback" is incorrectly marked as const in the GDVIRTUAL binding

### Tested versions

Exists in 4.5, and the current master branch (as of 09/11/25)

### System information

Godot v4.5.stable - Windows 10 (build 19045) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3080 (NVIDIA; 32.0.15.8088) - AMD Ryzen 9 5900X 12-Core Processor (24 threads) - 31.92 GiB memory

### Issue description

The GDVIRTUAL binding of the _instantiate_playback function of AudioStream marks it as const, when the actual function is non-const, making it impossible to override properly when using cpp bindings.

Binding (Incorrectly marked as const) : https://github.com/godotengine/godot/blob/6fd949a6dcbda94140200633394f2b4b99de8f6f/servers/audio/audio_stream.h#L173

Function(Non-const) : https://github.com/godotengine/godot/blob/6fd949a6dcbda94140200633394f2b4b99de8f6f/servers/audio/audio_stream.h#L185

### Steps to reproduce

N/A

### Minimal reproduction project (MRP)

N/A

Read servers/audio/audio_stream.h at the linked GDVIRTUAL binding and _instantiate_playback declarations, then compare their const qualifiers. Done means the binding and C++ function signature agree so a C++ override can work; no reproduction project or test is provided.

Written by the indexing model from the issue text.