Replace deprecated withOpacity in interactive_viewer.constrained.0.dart (flutter#177540)

Original PR that was intended to fix all examples:  
- flutter#177205  

It was later split into smaller PRs due to a major misunderstanding and
test failures caused by color values not matching exactly.

Similar PRs:  
- flutter#177374  
- flutter#177490  
- flutter#177540  
- flutter#177541  

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Author: AbdeMohlbi

examples/api/lib/widgets/interactive_viewer/interactive_viewer.constrained.0.dart

@@ -46,7 +46,9 @@ class ConstrainedExample extends StatelessWidget {
                 for (int column = 0; column < columnCount; column += 1)
                   Container(
                     height: 26,
-                    color: row % 2 + column % 2 == 1 ? Colors.white : Colors.grey.withOpacity(0.1),
+                    color: row % 2 + column % 2 == 1
+                        ? Colors.white
+                        : Colors.grey.withValues(alpha: 0.1),
                     child: Align(alignment: Alignment.centerLeft, child: Text('$row x $column')),
                   ),
               ],