Pin Zephyr SDK version

CI builds using the Zephyr SDK due to an update incompatible with our
example app. Before resolving the issue with newer SDKs this PR pins the
version of Zephyr used in CI.

Author: rauhul

.github/workflows/build-zephyr.yml

@@ -30,6 +30,7 @@ jobs:
         with:
           app-path: ${{ matrix.example }}
           toolchains: arm-zephyr-eabi
+          sdk-version: 0.17.0
 
       - name: Install Swift
         uses: ./.github/actions/install-swift