replace add-path with GITHUB_PATH env variable

Author: ladyada

.github/workflows/githubci.yml

@@ -24,7 +24,7 @@ jobs:
         mkdir $HOME/Arduino
         mkdir $HOME/Arduino/libraries
         curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | sh
-        echo "::add-path::$GITHUB_WORKSPACE/bin"
+        echo $GITHUB_WORKSPACE/bin >> $GITHUB_PATH
         
     - name: Install BSP and Libraries
       run: |