Bump pool to c40cc32eabecb9d60f1045d1403108d968805f9a

Changes:
```
> git log --format="%C(auto) %h %s" 7abe634..c40cc32
 https://dart.googlesource.com/pool.git/+/c40cc32 Merge pull request #56 from dart-lang/devoncarew-patch-1
 https://dart.googlesource.com/pool.git/+/5ce105e test against Dart 2.15
 https://dart.googlesource.com/pool.git/+/6e9885f switch to package:lints
 https://dart.googlesource.com/pool.git/+/430b860 rev to a dev version
 https://dart.googlesource.com/pool.git/+/a1e710d Update pubspec.yaml
 https://dart.googlesource.com/pool.git/+/4fcbdb9 Use latest CI setup, test on oldest supported SDK (#55)
 https://dart.googlesource.com/pool.git/+/005271c Merge pull request #54 from dart-lang/franklinyow-patch-1
 https://dart.googlesource.com/pool.git/+/b2dbf29 Update LICENSE
 https://dart.googlesource.com/pool.git/+/878759a Prepare to publish for stable null safety (#52)
 https://dart.googlesource.com/pool.git/+/c065054 Migrate to GitHub Actions (#51)
 https://dart.googlesource.com/pool.git/+/96b6734 Merge pull request #48 from dart-lang/pq-analyze
 https://dart.googlesource.com/pool.git/+/9688715 migrate from `dartanalyzer` to `dart analyze`

```

Diff: https://dart.googlesource.com/pool.git/+/7abe634002a1ba8a0928eded086062f1307ccfae~..c40cc32eabecb9d60f1045d1403108d968805f9a/
Change-Id: I10e7d7c2b8a4168770da5dfa8211bba9ce37a1f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244722
Commit-Queue: Devon Carew <devoncarew@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>

DEPS

@@ -135,7 +135,7 @@ vars = {
   "path_rev": "3d41ea582f5b0b18de3d90008809b877ff3f69bc",
   "platform_rev": "1ffad63428bbd1b3ecaa15926bacfb724023648c",
   "ply_rev": "604b32590ffad5cbb82e4afef1d305512d06ae93",
-  "pool_rev": "7abe634002a1ba8a0928eded086062f1307ccfae",
+  "pool_rev": "c40cc32eabecb9d60f1045d1403108d968805f9a",
   "process_rev": "56ece43b53b64c63ae51ec184b76bd5360c28d0b",
   "protobuf_rev": "c1eb6cb51af39ccbaa1a8e19349546586a5c8e31",
   "pub_rev": "51435efcd574b7bc18d47a5dd620cb9759dea8f8",