Test loading a PEM file from multiple threads #470

Job	Run time
compiler (gcc-7, ubuntu-20.04)	2m 59s
compiler (gcc-8, ubuntu-20.04)	2m 36s
compiler (gcc-9, ubuntu-20.04)	2m 43s
compiler (gcc-10, ubuntu-20.04)	3m 4s
compiler (gcc-11, ubuntu-22.04)	2m 40s
compiler (gcc-12, ubuntu-22.04)	3m 44s
compiler (gcc-13, ubuntu-22.04, ubuntu-toolchain-r/test)	3m 29s
compiler (clang-6.0, ubuntu-20.04)	1m 59s
compiler (clang-7, ubuntu-20.04)	1m 54s
compiler (clang-8, ubuntu-20.04)	2m 26s
compiler (clang-9, ubuntu-20.04)	3m 15s
compiler (clang-10, ubuntu-20.04)	3m 46s
compiler (clang-11, ubuntu-20.04)	3m 29s
compiler (clang-12, ubuntu-20.04)	3m 52s
compiler (clang-13, ubuntu-22.04)	2m 56s
compiler (clang-14, ubuntu-22.04)	3m 4s
compiler (clang-15, ubuntu-22.04, jammy)	2m 58s
compiler (clang-16, ubuntu-22.04, jammy)	3m 1s
	53m 55s

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