[dart2js] Change test suite on strong bot.
[dart2js] Change test suite on strong bot.

Not all co19 tests are migrated yet, so switch to a curated list.

Change-Id: I8f51c610382369216d50a3e9cb16a55cf2a06907
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143600
Reviewed-by: Sigmund Cherem <beaea8fd7d2a56555046ba4f362c8a93e3938576@google.com>
Commit-Queue: Joshua Litt <9f8daed1ab51574c9a48ffacb03e4a1adb4f880c@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk