analyze: Fix new lint on latest Flutter main

`flutter analyze` has started giving the following, which breaks CI:

   info • Unnecessary comparison to a boolean literal • lib/api/model/events.dart:1177:10 •
          no_literal_bool_comparisons
   info • Unnecessary comparison to a boolean literal • lib/model/channel.dart:158:13 •
          no_literal_bool_comparisons

We fixed the first one in the previous commit; this fixes the
second.

See discussion:
  https://chat.zulip.org/#narrow/channel/243-mobile-team/topic/CI.20on.20latest.20upstream/near/2228858

Author: chrisbobbe

lib/model/channel.dart

@@ -153,9 +153,10 @@ mixin ChannelStore on UserStore {
       case ChannelPostPolicy.any:             return true;
       case ChannelPostPolicy.fullMembers:     {
         if (!role.isAtLeast(UserRole.member)) return false;
-        return role == UserRole.member
-          ? hasPassedWaitingPeriod(user, byDate: byDate)
-          : true;
+        if (role == UserRole.member) {
+          return hasPassedWaitingPeriod(user, byDate: byDate);
+        }
+        return true;
       }
       case ChannelPostPolicy.moderators:      return role.isAtLeast(UserRole.moderator);
       case ChannelPostPolicy.administrators:  return role.isAtLeast(UserRole.administrator);