Preserve exit status of nix develop #45

Job	Run time
list-determinate-shells	14s
test-self (ubuntu-22.04)	23s
check (ubuntu-22.04)	21s
test-self (macos-13)	2m 6s
check (macos-13)	1m 47s
test-determinate-shells (cpp)	22s
test-determinate-shells (default)	1m 44s
test-determinate-shells (example)	21s
test-determinate-shells (go)	21s
test-determinate-shells (haskell)	49s
test-determinate-shells (hook)	21s
test-determinate-shells (javascript)	21s
test-determinate-shells (multi)	21s
test-determinate-shells (python)	21s
test-determinate-shells (rust)	35s
test-determinate-shells (scala)	35s
	11m 2s

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