Upgrade pub revision

$ git log --pretty=oneline 80ac76400ff58fde3c5a335d860d196c3febe837..HEAD
d15067931a6b671a1c9dcc98b5923347676269cf Add link to Flutter plugin docs to warning message (#2253)
61601357ac5857ddf7507ef71678cb9d15344f26 Improve error message when .dart_tool/package_config.json is missing (#2252)

Change-Id: I01726a0dd3d1c96301425d97294c7251ed4681fc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/124685
Reviewed-by: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>

Author: sigurdm

DEPS

@@ -117,7 +117,7 @@ vars = {
   "ply_rev": "604b32590ffad5cbb82e4afef1d305512d06ae93",
   "pool_tag": "1.3.6",
   "protobuf_rev": "3746c8fd3f2b0147623a8e3db89c3ff4330de760",
-  "pub_rev": "80ac76400ff58fde3c5a335d860d196c3febe837",
+  "pub_rev": "d15067931a6b671a1c9dcc98b5923347676269cf",
   "pub_semver_tag": "1.4.2",
   "quiver-dart_tag": "2.0.0+1",
   "resource_rev": "f8e37558a1c4f54550aa463b88a6a831e3e33cd6",