[web] Fix and enable editable_text_test.dart (#64516)

dev/bots/test.dart

@@ -92,7 +92,6 @@ const List<String> kWebTestFileKnownFailures = <String>[
   'test/widgets/selectable_text_test.dart',
   'test/widgets/color_filter_test.dart',
   'test/widgets/editable_text_cursor_test.dart',
-  'test/widgets/editable_text_test.dart',
   'test/material/animated_icons_private_test.dart',
   'test/material/data_table_test.dart',
   'test/cupertino/nav_bar_transition_test.dart',

packages/flutter/lib/src/widgets/editable_text.dart

@@ -1627,6 +1627,11 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     if (!_shouldCreateInputConnection) {
       return;
     }
+    if (widget.readOnly) {
+      // In the read-only case, we only care about selection changes, and reject
+      // everything else.
+      value = _value.copyWith(selection: value.selection);
+    }
     _receivedRemoteTextEditingValue = value;
     if (value.text != _value.text) {
       hideToolbar();