Direct GitHub-expression interpolation of `${{ steps.pnpm.outputs.bin_dest }}`
into the bash script let bash eat the backslashes in the Windows path
(`C:Usersrunneradminsetup-pnpmnode_modules.binbin/pnpm`), failing with
"No such file or directory". Forward the value via env so the path
reaches bash unmangled.
`pnpm self-update <version>` writes the target binary to
`${PNPM_HOME}/bin/`, leaving the bootstrap symlink at `${PNPM_HOME}/pnpm`
untouched. The `bin_dest` output was set to `${PNPM_HOME}`, so consumers
invoking `${{ steps.pnpm.outputs.bin_dest }}/pnpm` got the bootstrap
version (currently 11.0.4) instead of the version they requested.
PATH lookup hid the bug: `${PNPM_HOME}/bin` was prepended ahead of
`${PNPM_HOME}`, so `pnpm` resolved from PATH was the right one. Existing
version-respect tests only checked `pnpm --version`, not `bin_dest`.
Resolve `binDest` inside `runSelfInstaller` (target lives in
`${PNPM_HOME}/bin` after self-update, otherwise stays at `${PNPM_HOME}`)
and plumb it through to `setOutputs`. Add a regression test that invokes
`${bin_dest}/pnpm --version` directly across Linux/macOS/Windows.
