test: Add test case to verify installTime serialization

Author: dharambudh1

packages/package_info_plus/package_info_plus/example/ios/Flutter/AppFrameworkInfo.plist

@@ -21,6 +21,6 @@
   <key>CFBundleVersion</key>
   <string>1.0</string>
   <key>MinimumOSVersion</key>
-  <string>11.0</string>
+  <string>12.0</string>
 </dict>
 </plist>

packages/package_info_plus/package_info_plus/example/ios/Runner.xcodeproj/project.pbxproj

@@ -215,7 +215,7 @@
 		97C146E61CF9000F007C117D /* Project object */ = {
 			isa = PBXProject;
 			attributes = {
-				LastUpgradeCheck = 1300;
+				LastUpgradeCheck = 1510;
 				ORGANIZATIONNAME = "";
 				TargetAttributes = {
 					331C8080294A63A400263BE5 = {

packages/package_info_plus/package_info_plus/example/ios/Runner.xcodeproj/xcshareddata/xcschemes/Runner.xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1300"
+   LastUpgradeVersion = "1510"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"

packages/package_info_plus/package_info_plus/example/ios/Runner/AppDelegate.swift

@@ -1,7 +1,7 @@
 import UIKit
 import Flutter
 
-@UIApplicationMain
+@main
 @objc class AppDelegate: FlutterAppDelegate {
   override func application(
     _ application: UIApplication,

packages/package_info_plus/package_info_plus/test/package_info_test.dart

@@ -155,7 +155,7 @@ void main() {
       'packageName': 'io.flutter.plugins.mockpackageinfoexample',
       'version': '1.1',
       'buildNumber': '2',
-      'installTime': now,
+      'installTime': now.toIso8601String(),
     });
 
     final nextWeek = now.add(const Duration(days: 7));
@@ -176,7 +176,7 @@ void main() {
       'buildNumber': '2',
       'buildSignature': 'deadbeef',
       'installerStore': 'testflight',
-      'installTime': nextWeek,
+      'installTime': nextWeek.toIso8601String(),
     });
   });
 }