Mjcf Parser : Fix adding the sites frames #191

Job	Run time
ubuntu-latest - Env all Release	2m 0s
ubuntu-latest - Env all Debug	3m 13s
ubuntu-latest - Env all-py39 Release	39m 25s
ubuntu-latest - Env all-py39 Debug	40m 31s
macos-latest - Env all Release	2m 6s
macos-latest - Env all Debug	3m 0s
macos-latest - Env all-py39 Release	18m 38s
macos-latest - Env all-py39 Debug	16m 16s
macos-13 - Env all Release	3m 44s
macos-13 - Env all Debug	5m 54s
macos-13 - Env all-py39 Release	48m 39s
macos-13 - Env all-py39 Debug	49m 16s
windows-latest - Env all Release	1h 12m 45s
windows-latest - Env all-clang-cl Release	33m 6s
check-macos-linux-windows-pixi	1s
	5h 38m 34s

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