fix: bin_dest output points to self-updated pnpm, not bootstrap (#249)

* fix: bin_dest output points to self-updated pnpm, not bootstrap (#247)

`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.

* test(ci): pass bin_dest via env to survive Windows backslashes

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.

* build: rebuild dist with clean lockfile-matched deps

src/install-pnpm/index.ts

@@ -4,13 +4,15 @@ import runSelfInstaller from './run'
 
 export { runSelfInstaller }
 
-export async function install(inputs: Inputs) {
+export async function install(inputs: Inputs): Promise<string | undefined> {
   startGroup('Running self-installer...')
-  const status = await runSelfInstaller(inputs)
+  const { exitCode, binDest } = await runSelfInstaller(inputs)
   endGroup()
-  if (status) {
-    return setFailed(`Something went wrong, self-installer exits with code ${status}`)
+  if (exitCode) {
+    setFailed(`Something went wrong, self-installer exits with code ${exitCode}`)
+    return undefined
   }
+  return binDest
 }
 
 export default install