scripted-diff: Replace m_args with m_local_args in getarg_tests.cpp

Summary:

-BEGIN VERIFY SCRIPT-
git ls-files src/test/getarg_tests.cpp | xargs sed -i "s/m_args/m_local_args/g";
arc lint
-END VERIFY SCRIPT-

This is a backport of core#21244 [4/8]
https://github.com/bitcoin/bitcoin/pull/21244/commits/55c68e6f011ee604c8a65b9bca668eb4dec452aa

Depends on D10751

Test Plan: ninja check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10753