There is a typo in the actions/setup-go step which leads to the Go
version not being picked up correctly. Fix it.

Also enable testing with Go 1.17.

Use correct field to specify Go version in GitHub action

PR #66 updated the golang.org/x/sys dependency in go.mod but didn't
update go.sum. This leads to the following error on running go.test.sh:

    go: golang.org/x/sys@v0.0.0-20210630005230-0f9fa26af87c: missing go.sum entry; to add it:
    	go mod download golang.org/x/sys
    go: golang.org/x/sys@v0.0.0-20210630005230-0f9fa26af87c: missing go.sum entry; to add it:
    	go mod download golang.org/x/sys

Fix this by running go get -u && go mod tidy to update golang.org/x/sys
and clean up go.sum.

Update go.sum after golang.org/x/sys update

Update golang.org/x/sys for Go 1.18 on M1 Macs.

Support GNU/Hurd

go get golang.org/x/sys@latest && go mod tidy

Drop support of Go 1.15, 1.16 because of recent golang.org/x/sys which
stopped supporting them.

CI: add Go 1.20

deps: use a tagged version of golang.org/x/sys

Just log the output of IsTerminal in TestTerminal.

$ go test -v -run TestTerminal
=== RUN   TestTerminal
    isatty_others_test.go:13: os.Stdout: true
--- PASS: TestTerminal (0.00s)
PASS
ok  	github.com/mattn/go-isatty	0.160s
$ go test -v -run TestTerminal | cat
=== RUN   TestTerminal
    isatty_others_test.go:13: os.Stdout: false
--- PASS: TestTerminal (0.00s)
PASS
ok  	github.com/mattn/go-isatty	0.203s

tests: log value of IsTerminal