[flutter_image] [flutter_markdown] Do not use dynamic in an == operator override (#5298)

Fixes flutter/flutter#117838

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Author: srawlins

packages/flutter_image/lib/network.dart

@@ -223,7 +223,7 @@ class NetworkImageWithRetry extends ImageProvider<NetworkImageWithRetry> {
   }
 
   @override
-  bool operator ==(dynamic other) {
+  bool operator ==(Object other) {
     if (other.runtimeType != runtimeType) {
       return false;
     }

packages/flutter_markdown/lib/src/style_sheet.dart

@@ -659,7 +659,7 @@ class MarkdownStyleSheet {
 
   @override
   // ignore: avoid_equals_and_hash_code_on_mutable_classes
-  bool operator ==(dynamic other) {
+  bool operator ==(Object other) {
     if (identical(this, other)) {
       return true;
     }