ci: various fixes

[lars-reimann]

Closes #543.

Summary of Changes

• Fix Dependabot config
• Fix ESLint setup
• Update linter configurations

[github-actions]

MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ CREDENTIALS	secretlint	yes		no	3.68s
✅ GIT	git_diff	yes		no	1.06s
✅ JAVASCRIPT	eslint	1	0	0	7.46s
✅ JAVASCRIPT	prettier	1	0	0	0.6s
✅ JSON	eslint-plugin-jsonc	6	0	0	3.16s
✅ JSON	jsonlint	6		0	1.98s
✅ JSON	prettier	6	0	0	1.3s
✅ JSON	v8r	6		0	7.24s
✅ YAML	prettier	2	0	0	0.55s
✅ YAML	v8r	2		0	2.16s
✅ YAML	yamllint	2		0	0.15s

See errors details in artifact MegaLinter reports on CI Job page
Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff