package-and-qa fails consistently in master

An example is https://gitlab.com/gitlab-org/gitlab/-/jobs/1849278525

$ tooling/bin/find_change_diffs ${CHANGES_DIFFS_DIR}
CI_MERGE_REQUEST_PROJECT_PATH is missing.
CI_MERGE_REQUEST_IID is missing.
Exiting as this does not appear to be a merge request pipeline.
$ tooling/bin/qa/check_if_qa_only_spec_changes ${CHANGES_FILE} ${ONLY_QA_CHANGES_FILE} # collapsed multi-line command
tooling/bin/qa/check_if_qa_only_spec_changes:9:in `read': No such file or directory @ rb_sysopen - tmp/changed_files.txt (Errno::ENOENT)
	from tooling/bin/qa/check_if_qa_only_spec_changes:9:in `<main>'