[BugFix] TensorDictPrimer updates spec instead of overwriting (#2332) #2356

Job	Run time
unittests-meltingpot / linux-job	9m 4s
unittests-pettingzoo / linux-job	9m 23s
unittests-atari-dqn (3.9, 12.1) / linux-job	12m 7s
unittests-brax (3.11, 12.1) / linux-job	10m 1s
unittests-d4rl (3.9, 12.1) / linux-job	8m 15s
unittests-envpool (3.9, 12.1) / linux-job	8m 11s
unittests-gendgrl (3.9, 12.1) / linux-job	6m 37s
unittests-gym (3.9, 12.1) / linux-job	16m 18s
unittests-jumanji (3.9, 12.1) / linux-job	33m 28s
unittests-minari (3.9, 12.1) / linux-job	50m 40s
unittests-openx (3.9, 12.1) / linux-job	15m 56s
unittests-robohive (3.9, 12.1) / linux-job	44m 18s
unittests-roboset (3.9, 12.1) / linux-job	10m 40s
unittests-sklearn (3.9, 12.1) / linux-job	5m 29s
unittests-smacv2 (3.9, 12.1) / linux-job	11m 17s
unittests-vd4rl (3.9, 12.1) / linux-job	8m 59s
unittests-vmas (3.9, 12.1) / linux-job	12m 35s
	4h 33m 18s

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