Resolves several int -> uint conversion warnings. Warnings like the
following will be printed otherwise:
```
|
225 | uint shadow_type = flags & 0xF;
| ^
| gpu_shader_text_vert.glsl:17:22: Warning: some implementations
may not support implicit int -> uint conversions for `&'
operators; consider casting explicitly for portability
```
Pull Request: https://projects.blender.org/blender/blender/pulls/135890
e492794e1e