ci: force-reinstall nox in lint-python to fix pipx cache issue
Same class of problem as the Rust components: mise caches
~/.local/share/mise which has the nox install directory, but the
actual nox binary is a wrapper pointing to a uv/pipx-managed venv
that lives outside the cached path. On cache hit, mise skips
reinstall but the binary is missing.
Fix: mise install pipx:nox --force after mise-action.
