Add default Shader for ST9

- When opening the `HDRPTests` project, an error was logged in the Console complaining about an error with the `SpeedTree9` shader.
- It was due to the missing `default shader` of ST9 in the HDRP global settings. 
- Opening the project the first time: it complains about it, and add it to the settings. So then, the error disappears when reopening the project.

Author: YohannVaastUnity

Tests/SRPTests/Projects/HDRP_Tests/Assets/HDRPDefaultResources/HDRenderPipelineGlobalSettings.asset

@@ -378,6 +378,8 @@ MonoBehaviour:
           type: 3}
         m_DefaultSpeedTree8Shader: {fileID: -6465566751694194690, guid: 4819724840ee9444f9da841b477038ce,
           type: 3}
+        m_DefaultSpeedTree9Shader: {fileID: -6465566751694194690, guid: d81c74dd5f463104ca482aa23ef2c798,
+          type: 3}
     - rid: 120979388225814533
       type: {class: HDRenderPipelineRuntimeTextures, ns: UnityEngine.Rendering.HighDefinition,
         asm: Unity.RenderPipelines.HighDefinition.Runtime}