Fix path of the polkadot sha256 (#4458)

polkadot/.gitlab-ci.yml

@@ -201,7 +201,10 @@ test-build-linux-stable:
     - mkdir -p ./artifacts
     - VERSION="${CI_COMMIT_REF_NAME}" # will be tag or branch name
     - mv ./target/release/polkadot ./artifacts/.
-    - sha256sum ./artifacts/polkadot | tee ./artifacts/polkadot.sha256
+    - pushd artifacts
+    - sha256sum polkadot | tee polkadot.sha256
+    - shasum -c polkadot.sha256
+    - popd
     - EXTRATAG="$(./artifacts/polkadot --version |
         sed -n -r 's/^polkadot ([0-9.]+.*-[0-9a-f]{7,13})-.*$/\1/p')"
     - EXTRATAG="${CI_COMMIT_REF_NAME}-${EXTRATAG}-$(cut -c 1-8 ./artifacts/polkadot.sha256)"