tests: Added MIPS ISA test to learning_gem5/part1_tests.py

tests: Added MIPS ISA test to learning_gem5/part1_tests.py

Running these tests on the MIPS ISA was part of the old scons-based
scripts and was not present in the Python testlib framework (those
executed via `tests/main.py`). This has been migrated.

Jira: https://gem5.atlassian.net/browse/GEM5-109
Change-Id: Id87022e99ea83768710fb96b55136f777182fd43
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25803
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>