matrix/actions: add per-target timeout-minutes #206

Job	Run time
spelling	8s
validate commits	0s
Generate build matrix	8s
python linting	30s
bookworm - test-install	1m 30s
bookworm - 32 bit	1m 29s
fedora40 - test-install	1m 29s
noble - test-install	1m 40s
el9 - test-install	1m 41s
alpine - test-install	1m 14s
jammy - test-install	1m 29s
focal - py3.8	1m 18s
bookworm - gcc-12,content-s3,distcheck	1m 53s
fedora40 - clang-18	1m 29s
coverage	1m 31s
el8 - ascii	1m 30s
el8 - system,coverage	1m 40s
inception	1m 30s
flux-pam check	1m 29s
flux-sched check	1m 25s
flux-pmix check	1m 31s
flux-accounting check	1m 30s
Generate docker manifest	0s
	28m 4s

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