fix: drop patchPnpmEnv so standalone+self-update works on Windows

`patchPnpmEnv` prepended `dest/node_modules/.bin` to PATH before
spawning `pnpm install` / `pnpm store prune`. On Windows in standalone
mode, `.bin/pnpm.cmd` is an npm-created shim that always points at the
BOOTSTRAP pnpm (currently 11.0.4) — the binary npm linked when it
installed `@pnpm/exe` into `node_modules`. The self-updated pnpm
written by `pnpm self-update` lives at `$PNPM_HOME/bin`, which is
separately added to PATH via `addPath()` in install-pnpm.

When the user requested a pnpm version different from the bootstrap
under `standalone: true` on Windows, patchPnpmEnv's `.bin` entry
shadowed the self-updated `$PNPM_HOME/bin` and the action's internal
`pnpm install` ran on the bootstrap. On a pnpm 11.0.x bootstrap this
broke any 11.1+ install flag (e.g. `--no-runtime`), reporting:

    ERROR  Unknown option: 'runtime'

POSIX standalone got lucky because `.bin` and `$PNPM_HOME` resolve to
the same directory there. Non-standalone never tripped on this since
the `.bin/pnpm` symlink for a regular `pnpm` package keeps working
across self-updates.

Removed `patchPnpmEnv` and the now-empty `src/utils/` module.
`spawnSync` now inherits `process.env`, whose PATH is already
correctly fronted by `$PNPM_HOME/bin` and `$PNPM_HOME` via the
`addPath` calls in install-pnpm.

Added `standalone_windows_self_update` to test.yaml as a regression
guard: standalone on Windows + target 11.1.0 + `run_install` with
`--no-runtime`. With the previous code, the install would have run
under the bootstrap (11.0.4) and errored on the unknown flag.

Originally found while building pnpm/setup (the new combined
pnpm + runtime action).

README.md

@@ -48,7 +48,7 @@ If `run_install` is a YAML string representation of either an object or an array
 
 ### `cache_dependency_path`
 
-**Optional** (_type:_ `string`, _default:_ `pnpm-lock.yaml`) File path to the pnpm lockfile, whose contents hash will be used as a cache key. Accepts multiple paths delimited by newlines.
+**Optional** (_type:_ `string|string[]`, _default:_ `pnpm-lock.yaml`) File path to the pnpm lockfile, which contents hash will be used as a cache key.
 
 ### `package_json_file`
 
@@ -158,33 +158,6 @@ jobs:
 
 **Note:** You don't need to run `pnpm store prune` at the end; post-action has already taken care of that.
 
-### Cache dependencies from multiple lockfiles
-
-```yaml
-on:
-  - push
-  - pull_request
-
-jobs:
-  cache-and-install-multiple:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v6
-
-      - uses: pnpm/action-setup@v6
-        with:
-          version: 10
-          cache: true
-          cache_dependency_path: |
-            one/pnpm-lock.yaml
-            two/pnpm-lock.yaml
-          run_install: |
-            - cwd: one
-            - cwd: two
-```
-
 ## Notes
 
 This action does not setup Node.js for you, use [actions/setup-node](https://github.com/actions/setup-node) yourself.

action.yml

@@ -20,7 +20,7 @@ inputs:
     required: false
     default: 'false'
   cache_dependency_path:
-    description: File path to the pnpm lockfile, whose contents hash will be used as a cache key. Accepts multiple paths delimited by newlines.
+    description: File path to the pnpm lockfile, which contents hash will be used as a cache key
     required: false
     default: 'pnpm-lock.yaml'
   package_json_file: