build: Fix linter findings

.github/workflows/platformio-check.yaml

@@ -61,7 +61,7 @@ jobs:
         #!/bin/bash
         cacheSizePip=0
         if [ -d ${{ env.PIP_CACHE_FOLDER }} ]; then
-          cacheSizePip=$(echo $(du -s ${{ env.PIP_CACHE_FOLDER }}) | awk '{print $1}')
+          cacheSizePip=$(du -s ${{ env.PIP_CACHE_FOLDER }} | awk '{print $1}')
         fi
         cacheSizePlatformio=0
         if [ -d ${{ env.PLATFORMIO_CACHE_FOLDER }} ]; then