[ci] Don't emit warnings for normal CheckAdbTarget operations.

[jpobst]

Currently the start-emulator tasks emit 4 warnings for each invocation, related to the initial probing it does to see if an emulator is already running.

/Users/runner/work/1/s/build-tools/scripts/TestApks.targets(50,5): warning : * daemon not running; starting now at tcp:5037 [/Users/runner/work/1/s/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Emulator.csproj]
/Users/runner/work/1/s/build-tools/scripts/TestApks.targets(50,5): warning : * daemon started successfully [/Users/runner/work/1/s/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Emulator.csproj]
/Users/runner/work/1/s/build-tools/scripts/TestApks.targets(50,5): warning : adb: no devices/emulators found [/Users/runner/work/1/s/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Emulator.csproj]
/Users/runner/work/1/s/build-tools/scripts/TestApks.targets(50,5): warning :   Command /Users/runner/Library/Android/sdk/platform-tools/adb  shell getprop ro.build.version.sdk failed with exit code 1 [/Users/runner/work/1/s/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Emulator.csproj]

Write these messages as normal output instead of a warning.

Reduces CI reported warnings from 56 to 15.