Fix an incorrect scoped function call (introduced in #1093)

[mahaloz]

Description

In #1093, a call to add_context_layout_mapping was added without the self scoping, causing a crash when external plugins add a context pane to GEF. I triggered this in the latest version of d2d:

Python Exception <class 'NameError'>: name 'add_context_layout_mapping' is not defined
Error occurred in Python: name 'add_context_layout_mapping' is not defined

Checklist

• [X] My code follows the code style of this project.
• [X] My change includes a change to the documentation, if required.
• [X] If my change adds new code, adequate tests have been added.
• [X] I have read and agree to the CONTRIBUTING document.

Other Recommendations

If possible, I'd recommend adding a linter check as a requirement to the CI, so simple bugs like this can be caught :).

[github-actions[bot]]

🤖 Coverage update for 2066ca0e5d45cc316d073fcccd88cc2142b62cbf 🟢

	Old	New
Commit	6ddd7804453b563af28862a5bf85557bdfd3456e	2066ca0e5d45cc316d073fcccd88cc2142b62cbf
Score	71.6649%	71.6649% (0)