add sdk constraints where missing to prepare for nnbd flag flip (#68611)

dev/customer_testing/pubspec.yaml

@@ -2,7 +2,7 @@ name: customer_testing
 description: Tool to run the tests listed in the flutter/tests repository.
 
 environment:
-  sdk: any
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   args: 1.6.0

dev/integration_tests/android_semantics_testing/pubspec.yaml

 name: android_semantics_testing
 description: Integration testing library for Android semantics
+environment:
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   flutter:

dev/integration_tests/android_views/pubspec.yaml

 name: platform_views
 description: An integration test for embedded platform views
 version: 1.0.0+1
+environment:
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   flutter:

dev/integration_tests/hybrid_android_views/pubspec.yaml

 name: hybrid_platform_views
 description: An integration test for hybrid composition on Android
 version: 1.0.0+1
+environment:
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   flutter:

dev/integration_tests/image_loading/pubspec.yaml

 name: image_loading
 description: Integration testing library for Android semantics
+environment:
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   flutter:

dev/integration_tests/web_compile_tests/pubspec.yaml

 name: web_compile_tests
+environment:
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   flutter: