fix: openssl dependency on NixOS systems

Set the env variable `OPENSSL_NO_VENDOR` to `1` which forces the
`openssl-sys` crate to use `pkg-config` to find the local version of
openssl.

flake.nix

@@ -76,6 +76,8 @@
             pkgs.httpie
             pkgs.shellcheck
             pkgs.statix
+            pkgs.pkg-config
+            pkgs.openssl
             inputs'.holonix.packages.holochain
             inputs'.holonix.packages.lair-keystore
             inputs'.holonix.packages.hn-introspect
@@ -88,6 +90,8 @@
             pkgs.darwin.apple_sdk.frameworks.CoreFoundation
           ];
 
+          OPENSSL_NO_VENDOR = 1;
+
           shellHook = ''
             source ./scripts/influx.sh
             source ./scripts/telegraf.sh