wip deps: Upgrade Flutter to latest main, 3.11.0-11.0.pre.15

And update Flutter's supporting libraries to match, namely
package:collection.  (I've now further pinned down what's happening
with these upgrades done automatically by `flutter pub get`; see #85.)

Author: gnprice

pubspec.lock

@@ -181,10 +181,10 @@ packages:
     dependency: transitive
     description:
       name: collection
-      sha256: "4a07be6cb69c84d677a6c3096fcf960cc3285a8330b4603e0d463d15d9bd934c"
+      sha256: f092b211a4319e98e5ff58223576de6c2803db36221657b46c82574721240687
       url: "https://pub.dev"
     source: hosted
-    version: "1.17.1"
+    version: "1.17.2"
   convert:
     dependency: transitive
     description:
@@ -966,5 +966,5 @@ packages:
     source: hosted
     version: "3.1.2"
 sdks:
-  dart: ">=3.1.0-89.0.dev <4.0.0"
-  flutter: ">=3.11.0-2.0.pre.82"
+  dart: ">=3.1.0-129.0.dev <4.0.0"
+  flutter: ">=3.11.0-11.0.pre.15"

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: '>=3.1.0-89.0.dev <4.0.0'
-  flutter: '>=3.11.0-2.0.pre.82'
+  sdk: '>=3.1.0-129.0.dev <4.0.0'
+  flutter: '>=3.11.0-11.0.pre.15'
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions