[null-safety] update Dart SDK constraints (#69831)

diff --git a/packages/flutter/pubspec.yaml b/packages/flutter/pubspec.yaml
index d638f68..bb28012 100644
--- a/packages/flutter/pubspec.yaml
+++ b/packages/flutter/pubspec.yaml
@@ -5,7 +5,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_driver/pubspec.yaml b/packages/flutter_driver/pubspec.yaml
index 16df751..41755bb 100644
--- a/packages/flutter_driver/pubspec.yaml
+++ b/packages/flutter_driver/pubspec.yaml
@@ -5,7 +5,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   file: 6.0.0-nullsafety.4
diff --git a/packages/flutter_goldens/pubspec.yaml b/packages/flutter_goldens/pubspec.yaml
index 8e0226f..f728bba 100644
--- a/packages/flutter_goldens/pubspec.yaml
+++ b/packages/flutter_goldens/pubspec.yaml
@@ -2,7 +2,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-4.0.dev <2.12.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_goldens_client/pubspec.yaml b/packages/flutter_goldens_client/pubspec.yaml
index 1910763..770da79 100644
--- a/packages/flutter_goldens_client/pubspec.yaml
+++ b/packages/flutter_goldens_client/pubspec.yaml
@@ -2,7 +2,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-4.0.dev <2.12.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_test/pubspec.yaml b/packages/flutter_test/pubspec.yaml
index f639d6c..5eb398b 100644
--- a/packages/flutter_test/pubspec.yaml
+++ b/packages/flutter_test/pubspec.yaml
@@ -2,7 +2,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".