deps: Upgrade Flutter to latest main, 3.11.0-18.0.pre.81

And update Flutter's supporting libraries to match,
namely matcher, test, test_api, and test_core.

Author: gnprice

pubspec.lock

@@ -500,10 +500,10 @@ packages:
     dependency: transitive
     description:
       name: matcher
-      sha256: "6501fbd55da300384b768785b83e5ce66991266cec21af89ab9ae7f5ce1c4cbb"
+      sha256: "1803e76e6653768d64ed8ff2e1e67bea3ad4b923eb5c56a295c3e634bad5960e"
       url: "https://pub.dev"
     source: hosted
-    version: "0.12.15"
+    version: "0.12.16"
   material_color_utilities:
     dependency: transitive
     description:
@@ -833,26 +833,26 @@ packages:
     dependency: "direct dev"
     description:
       name: test
-      sha256: "4f92f103ef63b1bbac6f4bd1930624fca81b2574464482512c4f0896319be575"
+      sha256: "13b41f318e2a5751c3169137103b60c584297353d4b1761b66029bae6411fe46"
       url: "https://pub.dev"
     source: hosted
-    version: "1.24.2"
+    version: "1.24.3"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      sha256: daadc9baabec998b062c9091525aa95786508b1c48e9c30f1f891b8bf6ff2e64
+      sha256: "75760ffd7786fffdfb9597c35c5b27eaeec82be8edfb6d71d32651128ed7aab8"
       url: "https://pub.dev"
     source: hosted
-    version: "0.5.2"
+    version: "0.6.0"
   test_core:
     dependency: transitive
     description:
       name: test_core
-      sha256: "3642b184882f79e76ca57a9230fb971e494c3c1fd09c21ae3083ce891bcc0aa1"
+      sha256: "99806e9e6d95c7b059b7a0fc08f07fc53fabe54a829497f0d9676299f1e8637e"
       url: "https://pub.dev"
     source: hosted
-    version: "0.5.2"
+    version: "0.5.3"
   timing:
     dependency: transitive
     description:
@@ -982,5 +982,5 @@ packages:
     source: hosted
     version: "3.1.2"
 sdks:
-  dart: ">=3.1.0-155.0.dev <4.0.0"
-  flutter: ">=3.11.0-16.0.pre.11"
+  dart: ">=3.1.0-163.0.dev <4.0.0"
+  flutter: ">=3.11.0-18.0.pre.81"

pubspec.yaml

@@ -24,8 +24,8 @@ environment:
   # that by the time we want to release, these will have become stable.
   # TODO: Before general release, switch to stable Flutter and Dart versions,
   #   or pin exact versions: https://github.com/zulip/zulip-flutter/issues/15
-  sdk: '>=3.1.0-155.0.dev <4.0.0'
-  flutter: '>=3.11.0-16.0.pre.11'
+  sdk: '>=3.1.0-163.0.dev <4.0.0'
+  flutter: '>=3.11.0-18.0.pre.81'
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions