Revert "Bump actions to node 20 (#3461)" (#3462)

This reverts commit defeb8e52b.

As per https://github.com/actions/upload-artifact/issues/478 the new version of upload-artifact includes a breaking change.

.github/workflows/build_raspbian.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: [self-hosted, linux, ARM64]
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v3
         with:
           submodules: recursive
           ref: ${{github.event.pull_request.head.ref}}
@@ -37,7 +37,7 @@ jobs:
         id: version
 
       - name: Store binaries as an artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: firmware-raspbian-${{ steps.version.outputs.version }}.zip
           path: |