It's just a tool used by the developer; the onus is on the developer to ensure they don't infringe the licenses of the source code they incorporate in their software. Since Copilot makes it impossible to know where it's barfing code up from and what license that code is under, a developer who cares about not getting sued probably needs to avoid using Copilot.
The tool itself lacks agency, it did what it was programmed to do.
If you took the tool's suggestions and proceeded to published a derivative work, you may have infringed.
This really doesn't feel any different from P2P filesharing services. Rightsholders have targeted tool publishers in the past, because they are the largest single target and not anonymous; but ultimately the infringement is performed by the end user.