Without their own pubspecs, they belong to `_` project from the root
`pubspec.yaml`. As a result, once we bump the SDK version, these
scripts cannot be executed with the checked in sdk.

Note: when we bump the SDK version we also must bump the version in
the root pubspec, otherwise unreleased language experiments break.
Change-Id: Ie2ec35865a5966d6801de832a4b6ad312a24d277
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/436901


Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com>