fix CI builds

Signed-off-by: oppiliappan <[e-mail]>

.tangled/workflows/build.yml

···
     - cargo
     - rustc
     - rustfmt
+    - openssl
 
 steps:
   - name: build
     command: |
+       export PKG_CONFIG_PATH="${PKG_CONFIG_PATH:+$PKG_CONFIG_PATH:}$(nix build nixpkgs#openssl.dev --no-link --print-out-paths)/lib/pkgconfig"
        cargo build --all