Mjcf Parser : Fix adding the sites frames #228

Job	Run time
ubuntu-latest - Env all Release	39m 22s
ubuntu-latest - Env all Debug	3m 13s
ubuntu-latest - Env all-py39 Release	1m 51s
ubuntu-latest - Env all-py39 Debug	42m 18s
macos-latest - Env all Release	1m 59s
macos-latest - Env all Debug	3m 7s
macos-latest - Env all-py39 Release	21m 20s
macos-latest - Env all-py39 Debug	21m 34s
macos-13 - Env all Release	2m 59s
macos-13 - Env all Debug	45m 36s
macos-13 - Env all-py39 Release	53m 53s
macos-13 - Env all-py39 Debug	4m 40s
windows-latest - Env all Release	1h 17m 35s
windows-latest - Env all-clang-cl Release	33m 12s
check-macos-linux-windows-pixi	3s
	5h 52m 42s

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