kill test case fails on debian/arm64

Using my branch (see https://gitlab.com/rossburton/procps/-/jobs/13469109326) that adds more testing to CI, kill.test fails on debian/arm64:

Running /builds/rossburton/procps/testsuite/kill.test/kill.exp ...
FAIL: kill with SIGUSR1
ERROR: tcl error sourcing /builds/rossburton/procps/testsuite/kill.test/kill.exp.
ERROR: tcl error code NONE
ERROR: : spawn id exp16 not open
    while executing
"expect {
	-i $pipeproc_spawnid
        -re "$reg" { pass "$testname" }
        default { fail "$testname" }
		timeout { fail "$testname (timeout)" }
 ..."
    (procedure "expect_pipeproc_pass" line 4)
    invoked from within
"expect_pipeproc_pass "$test" "SIG SIGUSR2""
    (file "/builds/rossburton/procps/testsuite/kill.test/kill.exp" line 58)
    invoked from within
"source /builds/rossburton/procps/testsuite/kill.test/kill.exp"
    ("uplevel" body line 1)
    invoked from within
"uplevel #0 source /builds/rossburton/procps/testsuite/kill.test/kill.exp"
    invoked from within
"catch "uplevel #0 source $test_file_name" msg"
		=== kill Summary ===