Fix: Vulkan: Volume Workbench Tests

Due to an incorrect assumption float buffers were converted to sRGB
values when uploading to an sRGBA8 texture. This is done when rendering
flames in workbench and resulted in to bright renders.

This PR removes sRGB encoding when uploading float values to sRGBA8 textures.

Fixes:
- render/openvdb/fire
- render/openvdb/principled_blackbody
- render/openvdb/smoke_fire

Pull Request: https://projects.blender.org/blender/blender/pulls/146636

tests/python/workbench_render_tests.py

@@ -101,6 +101,8 @@ def main():
     test_dir_name = Path(args.testdir).name
     if test_dir_name.startswith('hair') and platform.system() == "Darwin":
         report.set_fail_threshold(0.050)
+    if test_dir_name.startswith('openvdb'):
+        report.set_fail_threshold(0.04)
 
     ok = report.run(args.testdir, args.blender, get_arguments, batch=args.batch)