bugfix: avoid spack race condition #175

Job	Run time
cuda_netlrts-linux-x86_64_buildonly	11m 49s
buildold_netlrts-linux-x86_64	17m 8s
charm4py_netlrts-linux-x86_64_tcp	6m 6s
changa_netlrts-linux-x86_64	6m 15s
doc	35s
mpi-linux-x86_64	10m 49s
mpi-linux-x86_64_syncft	11m 12s
multicore-darwin-x86_64_projections	1s
namd_netlrts-linux-x86_64	9m 3s
netlrts-darwin-x86_64	1s
netlrts-linux-i386	16m 46s
netlrts-linux-x86_64	15m 22s
netlrts-linux-x86_64_smp	21m 57s
netlrts-linux-x86_64_syncft	10m 3s
netlrts-win-x86_64_mingw64	17m 53s
shellcheck	6s
spack_ubuntu-latest	23m 4s
ucx-linux-x86_64_openpmix	16m 3s
spack_macos-12	1s
verbs-linux-x86_64_smp	14m 31s
	3h 28m 45s

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