In #1369, I mistakenly replaced the hash-bang lines in the two new
scripts with `#!/bin/sh`, missing that both files contain the Bash'ism
`[[`. Symptom as per
https://github.com/actions/checkout/actions/runs/5200323109/jobs/9378889172?pr=1369#step:12:5
__test__/verify-sparse-checkout.sh: 58: [[: not found
Let's change those hash-bang lines back to `#!/bin/bash`.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>