ci: bump macOS image on Github Actions to macos-11
The currently used image is getting deprecated and every user is advised
to switch to either macos-11 or macos-12. The link to upstream
issue/notification:
https://github.com/actions/virtual-environments/issues/5583
e3c8ba2dc5Jakub Konka committed on 7/15/2022, 2:56:21 PMparent577f9fd