Fix `ButtonStyleButton` ink well shape. (#100226)

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

@@ -367,7 +367,7 @@ class _ButtonStyleState extends State<ButtonStyleButton> with MaterialStateMixin
           splashFactory: resolvedSplashFactory,
           overlayColor: overlayColor,
           highlightColor: Colors.transparent,
-          customBorder: resolvedShape,
+          customBorder: resolvedShape.copyWith(side: resolvedSide),
           child: IconTheme.merge(
             data: IconThemeData(color: resolvedForegroundColor),
             child: Padding(

packages/flutter/test/material/elevated_button_test.dart

@@ -1554,6 +1554,51 @@ void main() {
 
     expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
   });
+
+  testWidgets('Ink Response shape matches Material shape', (WidgetTester tester) async {
+    // This is a regression test for https://github.com/flutter/flutter/issues/91844
+
+    Widget buildFrame({BorderSide? side}) {
+      return MaterialApp(
+       home: Scaffold(
+         body: Center(
+           child: ElevatedButton(
+             style: ElevatedButton.styleFrom(
+               side: side,
+               shape: const RoundedRectangleBorder(
+                 side: BorderSide(
+                   color: Color(0xff0000ff),
+                   width: 0,
+                  ),
+                ),
+             ),
+             onPressed: () { },
+             child: const Text('ElevatedButton'),
+           ),
+         ),
+       ),
+      );
+    }
+
+    const BorderSide borderSide = BorderSide(width: 10, color: Color(0xff00ff00));
+    await tester.pumpWidget(buildFrame(side: borderSide));
+    expect(
+      tester.widget<InkWell>(find.byType(InkWell)).customBorder,
+      const RoundedRectangleBorder(side: borderSide),
+    );
+
+    await tester.pumpWidget(buildFrame());
+    await tester.pumpAndSettle();
+    expect(
+      tester.widget<InkWell>(find.byType(InkWell)).customBorder,
+      const RoundedRectangleBorder(
+        side: BorderSide(
+          color: Color(0xff0000ff),
+          width: 0.0,
+        ),
+      ),
+    );
+  });
 }
 
 TextStyle _iconStyle(WidgetTester tester, IconData icon) {