Bump pub to 639536aa78f7382b4a948669bfdc283f830b2ae9

Changes:
```
> git log --format="%C(auto) %h %s" 710265b..639536a
 https://dart.googlesource.com/pub.git/+/639536aa Migrate to language 3.7, reformat, upgrade (4525)
 https://dart.googlesource.com/pub.git/+/a7fb7f2f Write .dart_tool/package_graph.json when writing package_config.json (4524)
 https://dart.googlesource.com/pub.git/+/531836e0 Use `sorted` from `package:collection` instead of custom util function (4516)
 https://dart.googlesource.com/pub.git/+/2d614417 Disallow activating packages with non-lowercase letters (4514)
 https://dart.googlesource.com/pub.git/+/a652ee48 Remove or replace unnecessary usages of late (4512)
 https://dart.googlesource.com/pub.git/+/4a2cbf3f Bump actions/stale from 9.0.0 to 9.1.0 in the github-actions group (4508)

```

Diff: https://dart.googlesource.com/pub.git/+/710265bae23ad5860f33287fba10b5c369f19a93..639536aa78f7382b4a948669bfdc283f830b2ae9/
Change-Id: Id5306c3619ce3ab63599556b03f747c4766035a0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/410761
Reviewed-by: Sarah Zakarias <[email protected]>
Commit-Queue: Sigurd Meldgaard <[email protected]>
Reviewed-by: Jonas Jensen <[email protected]>

Author: sigurdm

DEPS

@@ -142,7 +142,7 @@ vars = {
   "material_color_utilities_rev": "799b6ba2f3f1c28c67cc7e0b4f18e0c7d7f3c03e",
   "native_rev": "c817a5e41220de370cbea6e6445e63cdc7087544", # rolled manually while native assets are experimental
   "protobuf_rev": "610943a3bed70c1c2079af5fca02462df10d223f",
-  "pub_rev": "710265bae23ad5860f33287fba10b5c369f19a93", # rolled manually
+  "pub_rev": "639536aa78f7382b4a948669bfdc283f830b2ae9", # rolled manually
   "shelf_rev": "b39e61196ce555dc1d3a0c3da695228fa6bdebb8",
   "sync_http_rev": "47e6b264a209d0d806cfe9cdad8b6c69ce231986",
   "tar_rev": "5a1ea943e70cdf3fa5e1102cdbb9418bd9b4b81a",