allow mustache templates in job environment variables #10002

Job	Run time
validate commits	14s
Generate build matrix	8s
python linting	26s
spelling	7s
bookworm - test-install	6m 17s
bookworm - 32 bit	6m 18s
noble - test-install	1m 49s
el9 - test-install	6m 12s
alpine - test-install	6m 22s
fedora40 - test-install	5m 19s
jammy - test-install	1m 48s
focal - py3.8	3m 40s
bookworm - gcc-12,content-s3,distcheck	6m 18s
fedora40 - clang-18	6m 0s
coverage	6m 17s
el8 - ascii	6m 16s
el8 - test-install	6m 21s
el8 - system,coverage	6m 16s
inception	1m 50s
flux-accounting check	0s
flux-pmix check	0s
flux-sched check	0s
flux-pam check	0s
macos build only	0s
Generate docker manifest	1s
	1h 17m 59s

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