[ci] Roll Flutter to 9b3b9cf0893d54a40c2b6f8bc6c666ee77a8afa6 (#3128)

* [ci] Roll Flutter to 9b3b9cf0893d54a40c2b6f8bc6c666ee77a8afa6

* Re-add removed line
diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index dd5e807..04b248e 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-27f8ebdaed7078f311d456befae1c6236ba65fd8
+9b3b9cf0893d54a40c2b6f8bc6c666ee77a8afa6
diff --git a/packages/flutter_markdown/CHANGELOG.md b/packages/flutter_markdown/CHANGELOG.md
index 477eb94..a43c71b 100644
--- a/packages/flutter_markdown/CHANGELOG.md
+++ b/packages/flutter_markdown/CHANGELOG.md
@@ -1,5 +1,6 @@
-## NEXT
+## 0.6.13+1
 
+* Adjusts code to account for nullability change in Flutter SDK.
 * Updates the example to specify the import for `DropdownMenu`.
 
 ## 0.6.13
diff --git a/packages/flutter_markdown/lib/src/builder.dart b/packages/flutter_markdown/lib/src/builder.dart
index 293f12c..4e3c0c1 100644
--- a/packages/flutter_markdown/lib/src/builder.dart
+++ b/packages/flutter_markdown/lib/src/builder.dart
@@ -510,7 +510,7 @@
           _mergeInlineChildren(current.children, align),
           textAlign: align,
         );
-        _tables.single.rows.last.children!.add(child);
+        _ambiguate(_tables.single.rows.last.children)!.add(child);
       } else if (tag == 'a') {
         _linkHandlers.removeLast();
       }
@@ -859,4 +859,10 @@
       );
     }
   }
+
+  /// This allows a value of type T or T? to be treated as a value of type T?.
+  ///
+  /// We use this so that APIs that have become non-nullable can still be used
+  /// with `!` and `?` on the stable branch.
+  T? _ambiguate<T>(T? value) => value;
 }
diff --git a/packages/flutter_markdown/pubspec.yaml b/packages/flutter_markdown/pubspec.yaml
index 8f1259f..1e4cbb1 100644
--- a/packages/flutter_markdown/pubspec.yaml
+++ b/packages/flutter_markdown/pubspec.yaml
@@ -4,7 +4,7 @@
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.6.13
+version: 0.6.13+1
 
 environment:
   sdk: ">=2.12.0 <3.0.0"
diff --git a/packages/flutter_markdown/test/utils.dart b/packages/flutter_markdown/test/utils.dart
index f28ef29..7052210 100644
--- a/packages/flutter_markdown/test/utils.dart
+++ b/packages/flutter_markdown/test/utils.dart
@@ -157,7 +157,7 @@
 
   expect(table.children.length, rows);
   for (int index = 0; index < rows; index++) {
-    expect(table.children[index].children!.length, columns);
+    expect(_ambiguate(table.children[index].children)!.length, columns);
   }
 }
 
@@ -212,3 +212,9 @@
     }
   }
 }
+
+/// This allows a value of type T or T? to be treated as a value of type T?.
+///
+/// We use this so that APIs that have become non-nullable can still be used
+/// with `!` and `?` on the stable branch.
+T? _ambiguate<T>(T? value) => value;