The new Dart formatter needs to know the Dart language version of the
code it is formatting, and it reads that from a file in `.dart_tool`,
not `pubspec.yaml` directly. To avoid it failing to determine the
version and assuming the latest (which will almost always be wrong in
this repo):
- Adds a step to the `format` repo command to ensure that `pub get`
appears to have been run, and runs it if not, and
- To avoid `pub get` running in `format` in CI, adds a deps-fetching
step to the `repo_checks` task, as we have in other tasks that need to
`pub get`.
This should unblock the roll.
df0f423184