You'd like to run UI Tests and Unit Tests in separate builds without creating separate schemes for them.
Xcode 11 introduced the Test Plan feature, which allows you to separate the tests assigned to a scheme into multiple different sets.
To set up Test Plans with Bitrise's Xcode Test for iOS Step, add the -testPlan option to the Additional options for 'xcodebuild build test' call input, followed by the name of the Test Plan that you want to run.
You can then run different Xcode Test for iOS Steps in different builds using the same scheme but different test plans. This allows you to save time and avoid build timeouts.