CI: update SDK action to v3

No also check mirror hashes and badly formated init files

Signed-off-by: Paul Spooren <mail@aparcar.org>

.github/workflows/multi-arch-test-build.yml

@@ -83,7 +83,7 @@ jobs:
           echo "PACKAGES=$PACKAGES" >> $GITHUB_ENV
 
       - name: Build
-        uses: openwrt/gh-action-sdk@v1
+        uses: openwrt/gh-action-sdk@v3
         env:
           ARCH: ${{ matrix.arch }}-${{ env.BRANCH }}
           FEEDNAME: packages_ci