[gardening] pkg/dartdev tests failing on Windows

[dcharkes]

There are new test failures on Add support for patterns to replace null assert with cast fix...Resolve package pubspec of target for relevant dartdev commands.

The tests

pkg/dartdev/test/commands/compile_test RuntimeError (expected Pass)
pkg/dartdev/test/commands/doc_test RuntimeError (expected Pass)

are failing on configurations

unittest-asserts-release-win

@sigurdm @keertip there are two dartdev CLs in this range. The regression might have gone unnoticed as it's only on Windows.

Logs:

• https://dart-ci.appspot.com/log/pkg-win-release/unittest-asserts-release-win/24276/pkg/dartdev/test/commands/doc_test
• https://dart-ci.appspot.com/log/pkg-win-release/unittest-asserts-release-win/24276/pkg/dartdev/test/commands/compile_test

I have approved the failures, PTAL at the regression.