Update README.md

Author: eel76

README.md

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 # Traits for C++
 
-[![traits CI](https://github.com/VolumeGraphics/traits/actions/workflows/cmake-multi-platform.yml/badge.svg)](https://github.com/VolumeGraphics/traits/actions/workflows/cmake-multi-platform.yml)
+[![tests](https://github.com/VolumeGraphics/traits/actions/workflows/tests.yml/badge.svg)](https://github.com/VolumeGraphics/traits/actions/workflows/tests.yml)
 
 Define shared behavior in a non-intrusive way while preserving value semantics.