chore: enable local MQTT debug builds and disable MQTT_DEBUG in GitHub workflows

.github/workflows/pr-build-check.yml

@@ -15,6 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       OFFICIAL_MESHCORE_VERSION: ${{ vars.OFFICIAL_MESHCORE_VERSION }}
+      PLATFORMIO_BUILD_FLAGS: -UMQTT_DEBUG
     strategy:
       fail-fast: false
       matrix: