update rp2 actions/checkout to v4

Author: minyiky

.github/workflows/rp2_port.yml

@@ -11,7 +11,7 @@ jobs:
       matrix:
         board: [PICO]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: arm-none-eabi-gcc
       uses: carlosperate/[email protected]
       with: