Adding `NonisolatedNonsendingByDefault` to one target appears to apply it to all targets

[grynspan]

Is it reproducible with SwiftPM command-line tools: swift build, swift test, swift package etc?

• Confirmed reproduction steps with SwiftPM CLI. The description text must include reproduction steps with either of command-line SwiftPM commands, swift build, swift test, swift package etc.

Description

I added .enableUpcomingFeature("NonisolatedNonsendingByDefault") to one of Swift Testing's test targets and it appears to have caused the others to be built with the feature enabled (which broke them as they weren't prepared for the change.)

Expected behavior

.enableUpcomingFeature("NonisolatedNonsendingByDefault") affects only to the target it is applied to.

Actual behavior

.enableUpcomingFeature("NonisolatedNonsendingByDefault") appears to affect other test targets, if not all other targets.

Steps to reproduce

1. git clone git@github.com:swiftlang/swift-testing.git
2. git checkout jgrynspan/swiftpm-applies-nonisolated-nonsending-to-too-much
3. swift test --filter Exit

(All tests should pass.)

Swift Package Manager version/commit hash

Apple fork

Swift & OS version (output of swift --version ; uname -a)

Apple fork

[grynspan]

Looks like it applies it to targets with a dependency on the modified target, but it isn't inherited beyond that.