ci: test targeting old glibc

Author: branchseer

.github/workflows/ci.yml

@@ -57,6 +57,10 @@ jobs:
           RUSTFLAGS: '-D warnings --cfg tokio_unstable' # also update .cargo/config.toml
 
       - run: cargo test
+        if: ${{ matrix.os != 'ubuntu-latest' }}
+
+      - run: cargo-zigbuild test --target x86_64-unknown-linux-gnu.2.17
+        if: ${{ matrix.os == 'ubuntu-latest' }}
 
   lint:
     name: Lint