Update badges to point to gz-rendering9 branch (#1044)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Author: iche033

README.md

@@ -9,10 +9,10 @@
 
 Build | Status
 -- | --
-Test coverage | [![codecov](https://codecov.io/gh/gazebosim/gz-rendering/branch/main/graph/badge.svg)](https://codecov.io/gh/gazebosim/gz-rendering/branch/main)
-Ubuntu Noble  | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-ci-main-noble-amd64)](https://build.osrfoundation.org/job/gz_rendering-ci-main-noble-amd64)
-Homebrew      | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-ci-main-homebrew-amd64)](https://build.osrfoundation.org/job/gz_rendering-ci-main-homebrew-amd64)
-Windows       | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-main-win)](https://build.osrfoundation.org/job/gz_rendering-main-win)
+Test coverage | [![codecov](https://codecov.io/gh/gazebosim/gz-rendering/tree/gz-rendering9/graph/badge.svg)](https://codecov.io/gh/gazebosim/gz-rendering/tree/gz-rendering9)
+Ubuntu Noble  | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-ci-gz-rendering9-noble-amd64)](https://build.osrfoundation.org/job/gz_rendering-ci-gz-rendering9-noble-amd64)
+Homebrew      | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-ci-gz-rendering9-homebrew-amd64)](https://build.osrfoundation.org/job/gz_rendering-ci-gz-rendering9-homebrew-amd64)
+Windows       | [![Build Status](https://build.osrfoundation.org/buildStatus/icon?job=gz_rendering-9-win)](https://build.osrfoundation.org/job/gz_rendering-9-win)
 
 Gazebo Rendering is a C++ library designed to provide an abstraction
 for different rendering engines. It offers unified APIs for creating