deps: Update dart_style to 3.0.1, from 2.x

This results in the emitted code getting the new "tall" style,
which the Dart formatter added in order to get the Flutter project
on board with using the formatter.  See changelog:
  https://pub.dev/packages/dart_style/changelog#300

An upcoming Pigeon upgrade requires the upgraded dart_style,
prompting us to take this update.

This commit was produced by editing pubspec.yaml, then:

  $ flutter pub get
  $ tools/check --all-files --fix pigeon
  $ tools/check --all-files --fix build_runner
  $ tools/check --all-files --fix drift

(Plus a temporary commit before the build_runner step, because
build_runner would otherwise clobber part of pigeon's output.)

Author: gnprice

android/app/src/main/kotlin/com/zulip/flutter/Notifications.g.kt

@@ -1,4 +1,4 @@
-// Autogenerated from Pigeon (v22.7.2), do not edit directly.
+// Autogenerated from Pigeon (v22.7.4), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 @file:Suppress("UNCHECKED_CAST", "ArrayInDataClass")