github ci: drop Go 1.11

Contemporary x/sys/unix does not compile anymore with Go 1.11:

https://github.com/rfjakob/gocryptfs/runs/3362218517?check_suite_focus=true

+ GOOS=darwin
+ GOARCH=amd64
+ go build -tags without_openssl -o /dev/null
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/fcntl_darwin.go:11:9: undefined: fcntl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/fcntl_darwin.go:16:12: undefined: fcntl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/fcntl_darwin.go:22:12: undefined: fcntl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:21:9: undefined: ioctl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:30:9: undefined: ioctl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:39:9: undefined: ioctl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:49:9: undefined: ioctl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:61:9: undefined: ioctl
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/syscall_bsd.go:646:10: undefined: mmap
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/syscall_bsd.go:647:10: undefined: munmap
Error: ../../../go/pkg/mod/golang.org/x/sys@v0.0.0-20210817190340-bfb29a6856f2/unix/ioctl.go:61:9: too many errors
note: module requires Go 1.17make: *** [Makefile:44: ci] Error 2
Error: Process completed with exit code 2.

.github/workflows/ci.yml

@@ -11,7 +11,6 @@ jobs:
     strategy:
       matrix:
         go:
-          - "1.11.x" # Debian 10 "Buster"
           - "1.13.x" # Ubuntu 20.04 LTS "focal"
           - "1.15.x" # Debian 11 "Bullseye"
           - "1.16.x" # Golang upstream stable