Use preferred flutter version constraints (#1119)

pkgs/cupertino_http/example/pubspec.yaml

diff --git a/pkgs/cupertino_http/example/pubspec.yaml b/pkgs/cupertino_http/example/pubspec.yaml
index 026cb8a..8d61e62 100644
--- a/pkgs/cupertino_http/example/pubspec.yaml
+++ b/pkgs/cupertino_http/example/pubspec.yaml
@@ -7,7 +7,7 @@
 
 environment:
   sdk: ^3.2.0
-  flutter: ^3.16.0
+  flutter: '>=3.16.0'
 
 dependencies:
   cupertino_http:

pkgs/cupertino_http/pubspec.yaml

diff --git a/pkgs/cupertino_http/pubspec.yaml b/pkgs/cupertino_http/pubspec.yaml
index 644bf1b..2a819e1 100644
--- a/pkgs/cupertino_http/pubspec.yaml
+++ b/pkgs/cupertino_http/pubspec.yaml
@@ -1,5 +1,5 @@
 name: cupertino_http
-version: 1.3.0
+version: 1.3.1-wip
 description: >-
   A macOS/iOS Flutter plugin that provides access to the Foundation URL
   Loading System.
@@ -7,7 +7,7 @@
 
 environment:
   sdk: ^3.2.0
-  flutter: ^3.16.0  # If changed, update test matrix.
+  flutter: '>=3.16.0'  # If changed, update test matrix.
 
 dependencies:
   async: ^2.5.0