Implement fallback in case git diff does not work with merge-base

[nvuillam]

Fixes #3501
Fixes #3421

[github-actions]

🦙 MegaLinter status: ⚠️ WARNING

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ BASH	bash-exec	5		0	0.01s
✅ BASH	shellcheck	5		0	0.13s
✅ BASH	shfmt	5	0	0	0.18s
✅ COPYPASTE	jscpd	yes		no	3.88s
✅ DOCKERFILE	hadolint	128		0	15.14s
✅ JSON	jsonlint	19		0	0.23s
✅ JSON	v8r	21		0	26.93s
✅ MAKEFILE	checkmake	1		0	0.01s
⚠️ MARKDOWN	markdownlint	262	0	266	31.29s
✅ MARKDOWN	markdown-table-formatter	262	0	0	135.12s
✅ OPENAPI	spectral	1		0	1.63s
⚠️ PYTHON	bandit	209		64	3.08s
✅ PYTHON	black	209	0	0	5.06s
✅ PYTHON	flake8	209		0	1.52s
✅ PYTHON	isort	209	0	0	1.25s
✅ PYTHON	mypy	209		0	20.24s
✅ PYTHON	pylint	209		0	17.54s
✅ PYTHON	ruff	209	0	0	0.23s
✅ REPOSITORY	checkov	yes		no	40.25s
✅ REPOSITORY	git_diff	yes		no	0.19s
⚠️ REPOSITORY	grype	yes		1	24.0s
✅ REPOSITORY	secretlint	yes		no	17.49s
✅ REPOSITORY	trivy	yes		no	29.92s
✅ REPOSITORY	trivy-sbom	yes		no	11.68s
⚠️ REPOSITORY	trufflehog	yes		1	8.91s
✅ SPELL	cspell	686		0	29.31s
⚠️ SPELL	lychee	342		1	24.45s
✅ XML	xmllint	3	0	0	0.17s
✅ YAML	prettier	160	0	0	5.84s
✅ YAML	v8r	102		0	186.02s
✅ YAML	yamllint	161		0	2.09s

See detailed report in MegaLinter reports

MegaLinter is graciously provided by