Mjcf Parser : Fix adding the sites frames #224

Job	Run time
ubuntu-latest - Env all Release	15m 54s
ubuntu-latest - Env all Debug	3m 13s
ubuntu-latest - Env all-py39 Release	2m 8s
ubuntu-latest - Env all-py39 Debug	16m 3s
macos-latest - Env all Release	1m 34s
macos-latest - Env all Debug	3m 24s
macos-latest - Env all-py39 Release	10m 36s
macos-latest - Env all-py39 Debug	11m 8s
macos-13 - Env all Release	4m 39s
macos-13 - Env all Debug	15m 58s
macos-13 - Env all-py39 Release	15m 57s
macos-13 - Env all-py39 Debug	5m 13s
windows-latest - Env all Release	15m 50s
windows-latest - Env all-clang-cl Release	5m 11s
check-macos-linux-windows-pixi	2s
	2h 6m 50s

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