Fix some Flutter 3 lints

@@ -164,8 +164,10 @@ class MyAppState extends State<MyApp> with SingleTickerProviderStateMixin {
   }
 
   void _showSources() {
-    ul.launch(
-      'https://github.com/DavBfr/dart_pdf/blob/master/demo/lib/examples/${examples[_tab].file}',
+    ul.launchUrl(
+      Uri.parse(
+        'https://github.com/DavBfr/dart_pdf/blob/master/demo/lib/examples/${examples[_tab].file}',
+      ),
     );
   }
 

@@ -273,10 +273,6 @@ class _Percent extends pw.StatelessWidget {
     required this.size,
     required this.value,
     required this.title,
-    this.fontSize = 1.2,
-    this.color = green,
-    this.backgroundColor = PdfColors.grey300,
-    this.strokeWidth = 5,
   });
 
   final double size;
@@ -285,13 +281,13 @@ class _Percent extends pw.StatelessWidget {
 
   final pw.Widget title;
 
-  final double fontSize;
+  static const fontSize = 1.2;
 
-  final PdfColor color;
+  PdfColor get color => green;
 
-  final PdfColor backgroundColor;
+  static const backgroundColor = PdfColors.grey300;
 
-  final double strokeWidth;
+  static const strokeWidth = 5.0;
 
   @override
   pw.Widget build(pw.Context context) {

@@ -27,8 +27,9 @@ class App extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    const scrollbarTheme =
-        ScrollbarThemeData(isAlwaysShown: true, showTrackOnHover: true);
+    final scrollbarTheme = ScrollbarThemeData(
+      thumbVisibility: MaterialStateProperty.all(true),
+    );
 
     return MaterialApp(
       theme: ThemeData.light().copyWith(scrollbarTheme: scrollbarTheme),