remove ThemeData.cardColor from code background color when using material theme

Author: HosamHasanRamadan

packages/flutter_markdown/lib/src/style_sheet.dart

@@ -104,6 +104,7 @@ class MarkdownStyleSheet {
       p: theme.textTheme.bodyMedium,
       pPadding: EdgeInsets.zero,
       code: theme.textTheme.bodyMedium!.copyWith(
+        backgroundColor: theme.cardTheme.color,
         fontFamily: 'monospace',
         fontSize: theme.textTheme.bodyMedium!.fontSize! * 0.85,
       ),
@@ -280,6 +281,7 @@ class MarkdownStyleSheet {
       p: theme.textTheme.bodyMedium,
       pPadding: EdgeInsets.zero,
       code: theme.textTheme.bodyMedium!.copyWith(
+        backgroundColor: theme.cardTheme.color,
         fontFamily: 'monospace',
         fontSize: theme.textTheme.bodyMedium!.fontSize! * 0.85,
       ),

packages/flutter_markdown/test/style_sheet_test.dart

@@ -150,6 +150,7 @@ void defineTests() {
         expect(
             style.code!.fontSize, theme.textTheme.bodyMedium!.fontSize! * 0.85);
         expect(style.code!.fontFamily, 'monospace');
+        expect(style.code!.backgroundColor, theme.cardTheme.color);
 
         // H1
         expect(style.h1, theme.textTheme.headlineSmall);