68883 Fix a typo: “Its weight” instead of “It’s weight” (cla: yes, f: material design, framework, waiting for tree to go green)

68894 retry getting the main isolate (a: tests, cla: yes, framework)

68905 Remove nullOk parameter from Cupertino color resolution APIs (cla: yes, d: examples, f: cupertino, f: material design, framework, team)

68908 Remove nullOk from Scaffold.of and ScaffoldMessenger.of, create maybeOf for both (cla: yes, f: material design, framework, waiting for tree to go green)

68910 Remove nullOk parameter from Router.of and make it return a non-nullable value (cla: yes, framework, waiting for tree to go green)