nixos-rebuild-ng: make sure mypy in CI is running with its configuration

pkgs/by-name/ni/nixos-rebuild-ng/package.nix

@@ -134,14 +134,17 @@ python3Packages.buildPythonApplication rec {
         # NOTE: this is a passthru test rather than a build-time test because we
         # want to keep the build closures small
         linters = runCommand "${pname}-linters" { nativeBuildInputs = [ python-with-pkgs ]; } ''
+          export MYPY_CACHE_DIR="$(mktemp -d)"
           export RUFF_CACHE_DIR="$(mktemp -d)"
 
+          pushd ${src}
           echo -e "\x1b[32m## run mypy\x1b[0m"
-          mypy ${src}
+          mypy .
           echo -e "\x1b[32m## run ruff\x1b[0m"
-          ruff check ${src}
+          ruff check .
           echo -e "\x1b[32m## run ruff format\x1b[0m"
-          ruff format --check ${src}
+          ruff format --check .
+          popd
 
           touch $out
         '';