Fix czm_specularEnvironmentMaps datatype

[XiaoHu1994]

Description

The first parameter of czm_textureCube needs to be of type samplerCube

#ifdef SPECULAR_IBL
vec3 sampleSpecularEnvironment(vec3 cubeDir, float roughness)
{
#ifdef CUSTOM_SPECULAR_IBL
float lod = roughness * model_specularEnvironmentMapsMaximumLOD;
return czm_textureCube(model_specularEnvironmentMaps, cubeDir, lod).rgb;
#else
float lod = roughness * czm_specularEnvironmentMapsMaximumLOD;
return czm_textureCube(czm_specularEnvironmentMaps, cubeDir, lod).rgb;
#endif
}

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @XiaoHu1994!

✅ We can confirm we have a CLA on file for you.

[ggetz]

Thanks for the fix @XiaoHu1994!

@jjhembd can you please review?

• I think this may also warrant an update in CHANGES.md since this uniforms can be used in parts of the public API
• If this is ready to merge, please hold off until today's release as gone out.

[jjhembd]

Thanks @XiaoHu1994 for the fix!

@ggetz I don't see this uniform being used anywhere other than internally in ImageBasedLightingStageFS, so I don't think we need a mention in CHANGES.md.