nix: set CMAKE_PREFIX_PATH=

Author: nim65s

.github/workflows/test.yml

@@ -66,7 +66,7 @@ jobs:
         run: >
           nix shell   'nixpkgs#python3Packages.pinocchio' -c
           nix develop 'nixpkgs#python3Packages.pinocchio' -c
-          env | grep .=. >> $GITHUB_ENV
+          echo "CMAKE_PREFIX_PATH=${NIXPKGS_CMAKE_PREFIX_PATH}" >> $GITHUB_ENV
 
       # pip
       - if: matrix.pm == 'pip'