Today the App Store is offering me the Command Line Tools for Xcode 10.0 beta 1.
I do not recall ever signing up as a beta tester for any Apple software. Why do I get this update and how can I prevent such beta software from being accidentally installed on my system?
I have macOS 10.13.5 and Xcode 9.4. I also have MacPorts with clang 6.0 (newer than the one in Xcode, but it shouldn't interfere).
Update 2019-06-04: It is happening again, this time it is offering "Command Line Tools beta 1 for Xcode 11.0". This seems to be a mistake on Apple's part again (see the accepted answer).