build: Remove permissions of Preview GitHub action

[vorburger]

re. EndBug/pages-preview#20

[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	1		0	0.06s
✅ COPYPASTE	jscpd	yes		no	1.92s
✅ EDITORCONFIG	editorconfig-checker	1		0	0.01s
❌ REPOSITORY	checkov	yes		1	15.22s
✅ REPOSITORY	gitleaks	yes		no	0.22s
✅ REPOSITORY	git_diff	yes		no	0.01s
✅ REPOSITORY	grype	yes		no	16.31s
✅ REPOSITORY	kics	yes		no	40.49s
✅ REPOSITORY	secretlint	yes		no	0.92s
✅ REPOSITORY	trivy	yes		no	6.11s
✅ REPOSITORY	trivy-sbom	yes		no	1.7s
✅ REPOSITORY	trufflehog	yes		no	4.11s
✅ YAML	prettier	1	0	0	0.67s
✅ YAML	v8r	1		0	2.44s
✅ YAML	yamllint	1		0	0.48s

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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