Update `gitleaks` configuration in mega-linter

[unixorn]

Description

• Make gitleaks only check the current PR
• Add comments in test_*.py to make gitleaks ignore the test user data

License Acceptance

• [x] This repository is Apache version 2.0 licensed and by making this PR, I am contributing my changes to the repository under the terms of the Apache 2 license.

Type of changes

• [ ] Add/update a helper script
• [ ] Add/update link to an external resource like a blog post or video
• [ ] Bug fix
• [ ] New feature
• [x] Test updates
• [ ] Text cleanups/updates

Checklist

• [x] I have read the CONTRIBUTING document.
• [x] All new and existing tests pass.
• [ ] Any scripts added use #!/usr/bin/env interpreter instead of potentially platform-specific direct paths (#!/bin/sh is an allowed exception)
• [ ] Scripts added/updated in this PR are all marked executable.
• [ ] Scripts added/updated in this PR do not have a language file extension unless they are meant to be sourced and not run standalone. No one should have to know if a script was written in bash, python, ruby or whatever. Not including file extensions makes it easier to rewrite the script in another language later without having to change every reference to the previous version.
• [ ] I have confirmed that any links added or updated in my PR are valid.

[unixorn]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
❌ ACTION	actionlint	3		1	0.06s
✅ COPYPASTE	jscpd	yes		no	1.69s
✅ EDITORCONFIG	editorconfig-checker	7		0	0.05s
⚠️ MARKDOWN	markdownlint	1		12	0.68s
✅ MARKDOWN	markdown-table-formatter	1		0	0.43s
✅ PYTHON	bandit	1		0	1.18s
✅ PYTHON	black	2		0	2.0s
✅ PYTHON	flake8	2		0	1.1s
⚠️ PYTHON	isort	2		2	0.25s
✅ PYTHON	pylint	2		0	9.17s
✅ PYTHON	ruff	2		0	0.03s
❌ REPOSITORY	gitleaks	yes		5	0.45s
✅ REPOSITORY	git_diff	yes		no	0.01s
✅ REPOSITORY	grype	yes		no	11.65s
✅ REPOSITORY	secretlint	yes		no	0.84s
✅ REPOSITORY	trivy	yes		no	6.27s
✅ REPOSITORY	trivy-sbom	yes		no	4.95s
✅ REPOSITORY	trufflehog	yes		no	5.3s
✅ SPELL	lychee	4		0	0.65s
⚠️ YAML	prettier	3		1	0.62s
✅ YAML	v8r	3		0	3.06s
✅ YAML	yamllint	3		0	0.39s

See detailed report in MegaLinter reports _Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff_

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