scripted-diff: Replace m_args with m_local_args in getarg_tests.cpp
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 [[https://github.com/bitcoin/bitcoin/pull/21244 | 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

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