just: make release process a bit more robust

we now check that the required tools are available before attempting to
execute them

justfile

@@ -53,7 +53,12 @@ lint:
   uv run twine check --strict dist/*
   prek validate-config prek.toml
 
-release *release_name:
+pre_release_check: setup
+  test -x `which uv`
+  test -x `which git`
+  test -x `which fj`
+
+release *release_name: pre_release_check
   #!/usr/bin/env fish
   test -f {{ releasenotes }}; and set -l body "$(cat {{ releasenotes }})"; or begin echo Release notes are missing!; exit 2; end
   set -l tag (uv version --short --output-format text)