fix typo

Author: nicholascioli

.github/workflows/release-bins.yml

@@ -67,7 +67,7 @@ jobs:
             cp README.md LICENSE "release/$TARGET/dist"
 
             echo "Building release for $TARGET..."
-            nix build .#$TARGET
+            nix build .#$BUILD_TARGET
             cp result/bin/* "release/$TARGET/dist/"
           done