28138 Declare flutter_gdb as a Python 2 script (cla: yes)

28139 fuchsia: Improve FakeSession & add tests (affects: tests, cla: yes, waiting for tree to go green, platform-fuchsia, tech-debt)

28140 Use the suppressions script to source runtime suppressions in run_tests.py (cla: yes)

28142 Roll Dart SDK from 17c9a00cce20 to fecde133832e (1 revision) (cla: yes, waiting for tree to go green)

28143 Revert “[ci.yaml] Promote roller to blocking” (cla: yes, waiting for tree to go green)