set esp32 core version

Author: gigapod

.github/workflows/build-datalogger-iot.yml

@@ -56,7 +56,7 @@ jobs:
 
       # Install ESP32 - v3.0.7 - working as of June 2025 (latest versions fail for various reasons)
       - name: Arduino - Install ESP32 platform
-        run: arduino-cli core install esp32:esp32
+        run: arduino-cli core install esp32:esp32@3.1.3
 
       # install the libraries Flux uses
       - name: Install Flux dependant libraries.