I downloaded the last development snapshot from Swift.org - Download Swift, but, unlike the other snapshots, this one shows the following prompt when you try to run the .pkg:
The translation is the following:
Unable to open "swift-DEV..." because Apple cannot verify malware presence.
A software update is required...
It's the first time I'm seeing this prompt when installing a development snapshot. I'm running Big Sur 11.3.1 (20E241).