[CI] Fixed check for STM32

.github/workflows/main.yml

@@ -54,7 +54,7 @@ jobs:
           elif [[ "${{ contains(matrix.board, 'esp32') }}" == "true" ]]; then
             echo "::set-output name=index-url::--additional-urls https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json"
           
-          elif [[ "${{ contains(matrix.board, 'esp32') }}" == "true" ]]; then
+          elif [[ "${{ contains(matrix.board, 'STM32') }}" == "true" ]]; then
             echo "::set-output name=index-url::--additional-urls https://github.com/stm32duino/BoardManagerFiles/raw/master/STM32/package_stm_index.json"
           
           fi