Bump ai to 6a71aebe2b9c19e992dc6333a4111cdb8f9cd2b2

Changes:
```
> git log --format="%C(auto) %h %s" 2a5eb30..6a71aeb
 https://dart.googlesource.com/ai.git/+/6a71aeb run tests on windows, fix executable paths for dart/flutter (149)

```

Diff: https://dart.googlesource.com/ai.git/+/2a5eb30492c4231624ae954e93aa1491e4aca84f..6a71aebe2b9c19e992dc6333a4111cdb8f9cd2b2/
Change-Id: Ie3ff4bb84d42d87c1d401ce23301d8da68921d9d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/432480
Auto-Submit: Jake Macdonald <[email protected]>
Reviewed-by: Devon Carew <[email protected]>
Commit-Queue: Jake Macdonald <[email protected]>

Author: jakemac53

DEPS

@@ -129,7 +129,7 @@ vars = {
   ### /third_party/pkg dependencies
   # 'tools/rev_sdk_deps.dart' will rev pkg dependencies to their latest; put an
   # EOL comment after a dependency to instead pin at the current revision.
-  "ai_rev": "2a5eb30492c4231624ae954e93aa1491e4aca84f",
+  "ai_rev": "6a71aebe2b9c19e992dc6333a4111cdb8f9cd2b2",
   "core_rev": "635dfa32c261ba078438b74de397f2207904ca78",
   "dartdoc_rev": "4ceea6b8240bf1dd9694a170368264e40c67d66b",
   "ecosystem_rev": "8cebaf083e9107995811f1f0d2b40b570a0bbb66",