fix job submission to a multi-user instance over flux-proxy #7760

Job	Run time
python linting	43s
Generate build matrix	14s
validate commits	10s
spelling	9s
bookworm	12m 27s
bookworm - 32 bit	13m 47s
bookworm - gcc-12,content-s3,distcheck	14m 40s
bookworm - py3.11,clang-15	12m 39s
coverage	24m 6s
jammy - test-install	10m 3s
bookworm - test-install	9m 56s
focal - py3.8	12m 22s
el8	14m 57s
el8 - ascii	14m 41s
el8 - system,coverage	6m 15s
fedora34 - gcc-11.2,py3.9	13m 33s
fedora38 - gcc-13.1,py3.11	12m 12s
inception	24m 17s
flux-pmix check	16m 50s
flux-sched check	5m 49s
flux-accounting check	6m 41s
flux-pam check	5m 19s
Generate docker manifest	1s
	3h 51m 51s

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