🔨 Use PlatformIO Core 6.0 Dev for CI (MarlinFirmware#24194)

Author: ivankravets

.github/workflows/test-builds.yml

@@ -138,8 +138,9 @@ jobs:
 
     - name: Install PlatformIO
       run: |
-        pip install -U https://github.com/platformio/platformio-core/archive/v5.2.5.zip
-        platformio update
+        pip install -U platformio
+        pio upgrade --dev
+        pio pkg update --global
 
     - name: Run ${{ matrix.test-platform }} Tests
       run: |

docker/Dockerfile

@@ -1,7 +1,7 @@
 FROM python:3.9.0-buster
 
-RUN pip install -U https://github.com/platformio/platformio-core/archive/v5.2.5.zip
-RUN platformio update
+RUN pip install -U platformio
+RUN pio upgrade --dev
 # To get the test platforms
 RUN pip install PyYaml
 #ENV PATH /code/buildroot/bin/:/code/buildroot/tests/:${PATH}