[docs] update GitHub Actions badges in README (#6570)

* Update README.md

* Update README.md
Co-authored-by: James Lamb <jaylamb20@gmail.com>

---------
Co-authored-by: James Lamb <jaylamb20@gmail.com>

README.md

@@ -3,10 +3,10 @@
 Light Gradient Boosting Machine
 ===============================
 
-[![Python-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/workflows/Python-package/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions)
-[![R-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/workflows/R-package/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions)
-[![CUDA Version GitHub Actions Build Status](https://github.com/microsoft/LightGBM/workflows/CUDA%20Version/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions)
-[![Static Analysis GitHub Actions Build Status](https://github.com/microsoft/LightGBM/workflows/Static%20Analysis/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions)
+[![Python-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/python_package.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/python_package.yml)
+[![R-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/r_package.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/r_package.yml)
+[![CUDA Version GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/cuda.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/cuda.yml)
+[![Static Analysis GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/static_analysis.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/static_analysis.yml)
 [![Azure Pipelines Build Status](https://lightgbm-ci.visualstudio.com/lightgbm-ci/_apis/build/status/Microsoft.LightGBM?branchName=master)](https://lightgbm-ci.visualstudio.com/lightgbm-ci/_build/latest?definitionId=1)
 [![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/1ys5ot401m0fep6l/branch/master?svg=true)](https://ci.appveyor.com/project/guolinke/lightgbm/branch/master)
 [![Documentation Status](https://readthedocs.org/projects/lightgbm/badge/?version=latest)](https://lightgbm.readthedocs.io/)