make literals const for @immutable constructors (#29619)

packages/flutter/lib/src/material/time_picker.dart

@@ -965,9 +965,9 @@ class _DialPainter extends CustomPainter {
             textDirection: textDirection,
             onTap: label.onTap,
           ),
-          tags: <SemanticsTag>{
+          tags: const <SemanticsTag>{
             // Used by tests to find this node.
-            const SemanticsTag('dial-label'),
+            SemanticsTag('dial-label'),
           },
         );
         nodes.add(node);

packages/flutter/test/widgets/inherited_model_test.dart

@@ -241,7 +241,7 @@ void main() {
                 child: ABCModel( // The "inner" model
                   a: 100 + _a,
                   b: 100 + _b,
-                  aspects: <String>{'a'},
+                  aspects: const <String>{'a'},
                   child: Center(
                     child: Column(
                       mainAxisSize: MainAxisSize.min,