GPU: Better hash for specialization constants

Due to an error in the hash function the specialization constants hash
wasn't optimal. This PR fixes the hash function implementation by replacing
the addition with an xor.

Pull Request: https://projects.blender.org/blender/blender/pulls/120964

source/blender/gpu/intern/gpu_shader_create_info.hh

@@ -1233,7 +1233,7 @@ struct DefaultHash<Vector<gpu::shader::ShaderCreateInfo::SpecializationConstant:
   {
     uint64_t hash = 0;
     for (const gpu::shader::ShaderCreateInfo::SpecializationConstant::Value &value : key) {
-      hash = hash * 33 + value.u;
+      hash = hash * 33 ^ uint64_t(value.u);
     }
     return hash;
   }