Mjcf Parser : Fix adding the sites frames #188

Job	Run time
ubuntu-latest - Env all Release	1m 38s
ubuntu-latest - Env all Debug	1m 33s
ubuntu-latest - Env all-py39 Release	7m 31s
ubuntu-latest - Env all-py39 Debug	8m 11s
macos-latest - Env all Release	2m 3s
macos-latest - Env all Debug	6m 25s
macos-latest - Env all-py39 Release	5m 48s
macos-latest - Env all-py39 Debug	4m 5s
macos-13 - Env all Release	3m 35s
macos-13 - Env all Debug	3m 44s
macos-13 - Env all-py39 Release	11m 10s
macos-13 - Env all-py39 Debug	11m 34s
windows-latest - Env all Release	19m 11s
windows-latest - Env all-clang-cl Release	12m 8s
check-macos-linux-windows-pixi	3s
	1h 38m 39s

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