fix handling of `\n` in submission cli `--add-file=` option #9997

Job	Run time
validate commits	14s
python linting	35s
Generate build matrix	11s
spelling	6s
bookworm - test-install	12m 8s
bookworm - 32 bit	13m 0s
noble - test-install	13m 14s
el9 - test-install	12m 18s
alpine - test-install	12m 32s
fedora40 - test-install	11m 55s
jammy - test-install	11m 44s
focal - py3.8	16m 48s
bookworm - gcc-12,content-s3,distcheck	19m 44s
fedora40 - clang-18	16m 37s
coverage	29m 46s
el8 - ascii	19m 28s
el8 - test-install	13m 36s
el8 - system,coverage	7m 43s
inception	22m 25s
macos build only	2m 53s
flux-pam check	4m 21s
flux-accounting check	4m 46s
flux-pmix check	13m 36s
flux-sched check	6m 55s
Generate docker manifest	1s
	4h 26m 36s

Provide feedback