fix job submission to a multi-user instance over flux-proxy #7759

Job	Run time
python linting	41s
Generate build matrix	7s
validate commits	17s
spelling	8s
bookworm	12m 11s
bookworm - 32 bit	12m 59s
bookworm - gcc-12,content-s3,distcheck	14m 48s
bookworm - py3.11,clang-15	12m 10s
coverage	23m 36s
jammy - test-install	9m 46s
bookworm - test-install	17m 30s
focal - py3.8	23m 49s
el8	15m 2s
el8 - ascii	14m 36s
el8 - system,coverage	6m 19s
fedora34 - gcc-11.2,py3.9	13m 12s
fedora38 - gcc-13.1,py3.11	23m 22s
inception	15m 47s
flux-sched check	8m 36s
flux-pmix check	21m 9s
flux-accounting check	4m 4s
flux-pam check	4m 5s
Generate docker manifest	1s
	4h 14m 15s

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