buildah: 0.11 -> 0.12

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah -h` got 0 exit code
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah --help` got 0 exit code
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah help` got 0 exit code
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah -v` and found version 0.12
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah --version` and found version 0.12
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah -h` and found version 0.12
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah --help` and found version 0.12
- ran `/nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin/bin/buildah help` and found version 0.12
- found 0.12 with grep in /nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin
- found 0.12 in filename of file in /nix/store/1by5s8x42fdb4xfz61h8a48dfw9vbdkp-buildah-0.12-bin