Fix step "Test ssh connectivity" in coverage

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

Author: NobodyXu

.github/workflows/coverage.yml

@@ -29,6 +29,8 @@ jobs:
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@cargo-llvm-cov
       - run: |
+          # Wait for startup of openssh-server
+          sleep 30
           chmod 600 .test-key
           mkdir /tmp/openssh-rs
           ssh -i .test-key -v -p 2222 -l test-user openssh -o StrictHostKeyChecking=accept-new -o UserKnownHostsFile=/tmp/openssh-rs/known_hosts whoami