Add postgres singularity option #1989

Job	Run time
deploy	17s
test (3.8, lint)	43s
test (3.8, lint_docs)	1m 32s
test (3.8, mypy)	45s
test (3.8, unit-quick)	18m 18s
test (3.8, unit-diagnostic-servebasic-gx-dev)	4m 7s
test (3.8, unit-nonredundant-noclientbuild-noshed-gx-2205)	20m 15s
test (3.8, unit-nonredundant-noclientbuild-noshed-gx-231)	24m 35s
test (3.8, unit-nonredundant-noclientbuild-noshed-gx-dev)	24m 47s
test (3.8, unit-nonredundant-noclientbuild-noshed-nogx)	1h 15m 18s
test (3.8, unit-diagnostic-serveclientcmd)	4m 10s
test (3.11, lint)	40s
test (3.11, mypy)	42s
test (3.11, unit-quick)	17m 42s
	3h 13m 51s

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