nix: set CMAKE_PREFIX_PATH=

Author: nim65s

.github/workflows/test.yml

@@ -66,7 +66,9 @@ jobs:
         run: >
           nix shell   'nixpkgs#python3Packages.pinocchio' -c
           nix develop 'nixpkgs#python3Packages.pinocchio' -c
-          env | grep .=. >> $GITHUB_ENV
+          env | grep .=. | tee $GITHUB_ENV
+      - if: matrix.pm == 'nix'
+        run: echo "CMAKE_PREFIX_PATH=${NIXPKGS_CMAKE_PREFIX_PATH}" >> $GITHUB_ENV
 
       # pip
       - if: matrix.pm == 'pip'