87872 Fix compile error in SliverAppBar sample code (framework, f: material design, cla: yes, waiting for tree to go green)

87873 Updated skipped tests for scheduler directory. (team, framework, cla: yes, tech-debt, skip-test)

87874 Updated skipped tests for services directory. (team, framework, cla: yes, tech-debt, skip-test)

87879 Updated skipped tests for widgets directory. (team, framework, cla: yes, will affect goldens, tech-debt, skip-test)

87880 Updated skipped tests for flutter_test directory. (a: tests, framework, cla: yes, skip-test)

87901 Changing ElevatedButton.child to be non-nullable (framework, f: material design, cla: yes)