base-stats,python: Add missing "group" in `_prepare_stats`
base-stats,python: Add missing "group" in `_prepare_stats`

Change-Id: Idb25185e1d29ac9fd8c0503d55b56e0568a61d1f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42704
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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