Use development version of PlatformIO (#18724)

.github/workflows/test-builds.yml

 
     - name: Install PlatformIO
       run: |
-        pip install -U https://github.com/platformio/platformio-core/archive/master.zip
+        pip install -U https://github.com/platformio/platformio-core/archive/develop.zip
         platformio update
 
     - name: Check out the PR