Stop the terminal tests reading a pty nobody opened (closes #126)

On Linux, pty.Open of github.com/creack/pty v1.1.24 passes the address
of a local variable to ioctl as a plain number, through a function
call. When Go moved the goroutine's stack in between, the kernel wrote
the pty's number to the old place, and pty.Open opened /dev/pts/0,
another terminal. secret rm wrote there, and the test read a terminal
no program had open, which never ends. Require the commit on the
library's main branch that passes a pointer; no release has it yet.

Both terminal tests now stop reading when their one-minute context
ends, and fail saying what was still waiting.

Model: opus-5-5

internal/cli/integration_test.go

@@ -2603,10 +2603,7 @@ func TestRemoveWithoutTerminalFailsAtOnce(t *testing.T) {
 // tty is the end a program uses as its terminal, and ptmx the end the test
 // reads what the terminal shows from and types into. Reading ptmx stops at
 // the context's deadline, when secret rm is killed too, so a terminal that
-// stays open fails the test then instead of hanging it. The deadline works
+// stays open fails the test then instead of hanging it.
-// only while ptmx stays non-blocking, as pty.Open of the github.com/creack/pty
-// commit in go.mod leaves it: calling ptmx.Fd() or going back to v1.1.24
-// makes the read ignore the deadline, without any error.
 
 // TestRemoveIgnoresTerminalOnStdout runs `echo y | secret rm x` at a
 // terminal. stdin is a pipe, so nobody can answer there, and the command