fix: pnpm self-update binary shadowed by bootstrap on PATH (#230)

Problem
pnpm self-update installs the target version to PNPM_HOME/bin/pnpm, but the bootstrap binary at PNPM_HOME/pnpm has higher PATH precedence because addPath(pnpmHome) was called after addPath(pnpmHome/bin). @actions/core's addPath prepends, so the later call wins — the bootstrap version shadows the self-updated binary.

Fix
Swap the addPath call order so PNPM_HOME/bin (where self-update puts the target binary) has higher PATH precedence. The bootstrap pnpm is invoked via absolute path, so this doesn't affect the bootstrap step.

Author: oniani1