Fix behavior change due to incorrect initial floating setting (#55651)

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

@@ -1915,8 +1915,10 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
     super.initState();
 
     final bool labelIsInitiallyFloating = widget.decoration.floatingLabelBehavior == FloatingLabelBehavior.always
-        // ignore: deprecated_member_use_from_same_package
-        || (widget.decoration.hasFloatingPlaceholder && widget._labelShouldWithdraw);
+        || (widget.decoration.floatingLabelBehavior != FloatingLabelBehavior.never &&
+            // ignore: deprecated_member_use_from_same_package
+            widget.decoration.hasFloatingPlaceholder &&
+            widget._labelShouldWithdraw);
 
     _floatingLabelController = AnimationController(
       duration: _kTransitionDuration,

packages/flutter/test/material/input_decorator_test.dart

@@ -3910,4 +3910,18 @@ void main() {
     expect(tester.getTopLeft(find.text('label')).dy, -4.0);
   });
 
+  testWidgets('InputDecorator floating label obeys floatingLabelBehavior', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      buildInputDecorator(
+        decoration: const InputDecoration(
+          labelText: 'label',
+          floatingLabelBehavior: FloatingLabelBehavior.never,
+        ),
+      ),
+    );
+
+    // Passing floating behavior never results in a dy offset of 20
+    // because the label is not initially floating.
+    expect(tester.getTopLeft(find.text('label')).dy, 20.0);
+  });
 }