python: debug, fix Mapping import
python: debug, fix Mapping import

Change "collections.Mapping" to "collections.abc.Mapping".
"collections.Mapping" was an alias, it is deprecated starting from Python 3.3, and it will be removed in Python 3.10.

Change-Id: Ic257e3c5206eb3d48d4eed85a93fac48bd3b8dc4
Signed-off-by: Adrian Herrera <0f7a8031d49cb35713856aa725eb9889c7627fd9@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43023
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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