Don't change the height of the Textfield's labelStyle when it focused. (#141943)

Fixes #141448

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

@@ -2123,9 +2123,9 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 
     return themeData.textTheme.titleMedium!
       .merge(widget.baseStyle)
-      .copyWith(height: 1)
       .merge(defaultTextStyle)
-      .merge(style);
+      .merge(style)
+      .copyWith(height: 1);
   }
 
   TextStyle _getHelperStyle(ThemeData themeData, InputDecorationTheme defaults) {

packages/flutter/test/material/input_decorator_test.dart

@@ -7022,4 +7022,29 @@ testWidgets('OutlineInputBorder with BorderRadius.zero should draw a rectangular
       reason: 'clamp is expected',
     );
   });
+
+  testWidgets('Ensure the height of labelStyle remains unchanged when TextField is focused.', (WidgetTester tester) async {
+    final FocusNode focusNode = FocusNode();
+    addTearDown(focusNode.dispose);
+    final ThemeData theme = ThemeData(useMaterial3: true);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: theme,
+        home: Material(
+          child: TextField(
+            focusNode: focusNode,
+            decoration: const InputDecoration(
+              labelText: 'label',
+            ),
+          ),
+        ),
+      ),
+    );
+    final TextStyle beforeStyle = getLabelStyle(tester);
+    // Focused.
+    focusNode.requestFocus();
+    await tester.pumpAndSettle();
+    expect(getLabelStyle(tester).height, beforeStyle.height);
+  });
 }