Depend on plugin_platform_interface from GIT

Author: mvanbeusekom

packages/url_launcher/url_launcher/example/pubspec.yaml

@@ -16,7 +16,10 @@ dev_dependencies:
   mockito: ^4.1.1
   # TODO (mvanbeusekom): Update to use pub.dev once 1.10.0-nullsafety released.
   plugin_platform_interface:
-    path: ../../../plugin_platform_interface
+    git:
+      url: https://github.com/flutter/plugins.git
+      ref: nnbd
+      path: packages/plugin_platform_interface
 
 flutter:
   uses-material-design: true