"Check custom startup script" sporadic failures in Github Actions CI

[lmakarov]

This has been quite an annoyance recently. This test fails sporadically in CI. I'm not able to reproduce it locally.
Re-running CI jobs helps, but this keeps happening over and over again. Does not depend on the architecture or PHP version.

not ok 10 Check custom startup script
# (in test file /home/runner/work/service-cli/service-cli/tests/test.bats, line 403)
#   `[[ ${status} == 0 ]]' failed
# make[1]: Entering directory '/home/runner/work/service-cli/service-cli/7.4'
# docker rm -vf docksal-cli-7.4-5129ceb >/dev/null 2>&1 || true
# docker create --name docksal-cli-7.4-5129ceb  -v /home/docker -e XDEBUG_ENABLED -e SECRET_BLACKFIRE_CLIENT_ID -e SECRET_BLACKFIRE_CLIENT_TOKEN -e SECRET_SSH_PRIVATE_KEY -e SECRET_PLATFORMSH_CLI_TOKEN -e SECRET_TERMINUS_TOKEN docksal/cli:php7.4-build-5129ceb-amd64
# 706bf6cfcc1a50737abc51a7c1335e1f9063c6a7559e5861ba689[31](https://github.com/docksal/service-cli/runs/6040742470?check_suite_focus=true#step:7:31)55d7919e5
# docker cp ../tests/. docksal-cli-7.4-5129ceb:/var/www/
# docker start docksal-cli-7.4-5129ceb
# docksal-cli-7.4-5129ceb
# make[1]: Leaving directory '/home/runner/work/service-cli/service-cli/7.4'
# 
# Note: ignore the lines between "...failed" above and here
# 
# Status: 0
# Output:
# ================================================================
# cat: /tmp/test-startup.txt: No such file or directory
# ================================================================