fix: use correct pgrx 0.16.1 for VectorChord v1.1.0

VectorChord v1.1.0 (tag c68a6ae) uses pgrx =0.16.1 in Cargo.toml,
not 0.17.0. The version mismatch caused cargo-pgrx package to crash
during CI. Match the actual dependency versions.

Author: h0lybyte

nix/ext/vectorchord.nix

@@ -8,8 +8,8 @@
 let
   pname = "vchord";
   version = "1.1.0";
-  rustVersion = "1.90.0";
-  pgrxVersion = "0.17.0";
+  rustVersion = "1.88.0";
+  pgrxVersion = "0.16.1";
 
   cargo = rust-bin.stable.${rustVersion}.default;
   mkPgrxExtension = callPackages ../cargo-pgrx/mkPgrxExtension.nix {