Fix GTSAM version setting #2538

Job	Run time
ubuntu-clang-deprecated Debug	34m 30s
ubuntu-clang-deprecated Release	29m 27s
ubuntu-clang-quaternions Debug	28m 35s
ubuntu-clang-quaternions Release	29m 37s
ubuntu-clang-tbb Debug	31m 37s
ubuntu-clang-tbb Release	32m 31s
ubuntu-clang-cayleymap Debug	40m 52s
ubuntu-clang-cayleymap Release	31m 59s
ubuntu-clang-system-libs Debug	41m 18s
ubuntu-clang-system-libs Release	35m 56s
ubuntu-no-boost Debug	30m 19s
ubuntu-no-boost Release	34m 52s
ubuntu-no-unstable Debug	27m 31s
ubuntu-no-unstable Release	27m 37s
	7h 36m 41s

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