Allow linsolve to be \ #1171

Job	Run time
test (RootFinding, 1.10, ubuntu-latest)	33m 51s
test (RootFinding, 1.10, macos-latest)	47m 50s
test (RootFinding, 1.10, windows-latest)	36m 56s
test (NLLSSolvers, 1.10, ubuntu-latest)	7m 40s
test (NLLSSolvers, 1.10, macos-latest)	15m 24s
test (NLLSSolvers, 1.10, windows-latest)	10m 39s
test (23TestProblems, 1.10, ubuntu-latest)	8m 8s
test (23TestProblems, 1.10, macos-latest)	16m 58s
test (23TestProblems, 1.10, windows-latest)	10m 39s
test (Wrappers, 1.10, ubuntu-latest)	7m 49s
test (Wrappers, 1.10, macos-latest)	15m 7s
test (Wrappers, 1.10, windows-latest)	10m 28s
test (Miscellaneous, 1.10, ubuntu-latest)	10m 36s
test (Miscellaneous, 1.10, macos-latest)	18m 26s
test (Miscellaneous, 1.10, windows-latest)	13m 13s
	4h 23m 44s

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