Revert "Use Dart 2.9.3 for Node tests and releases (#1105)"
Revert "Use Dart 2.9.3 for Node tests and releases (#1105)"

This reverts commit bdef3aced33141f374c3bfec4f0cdeb68722e454. It turns
out that Dart 2.10 was not the cause of #1104.

sass/dart-sass,sass/dart-sass