fix(release): check for release_created == 'true'

[martinohmann]

The docs of the release-please-action state that release_created is false if no release was created.

https://github.com/googleapis/release-please-action?tab=readme-ov-file#root-component-outputs

This is incorrect, release_created is empty in this case. An empty string in the enable attribute leads to an Invalid value error:

https://github.com/Bonial-International-GmbH/sops-check/actions/runs/12117567635/job/33780291842

We'll explicitly compare release_created to 'true' to make sure the result can only be true or false, but nothing else.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	3		0	0.06s
✅ DOCKERFILE	hadolint	1		0	0.18s
✅ GO	golangci-lint	yes		no	67.67s
✅ JSON	jsonlint	3		0	0.4s
✅ JSON	prettier	3		0	0.54s
✅ JSON	v8r	3		0	2.05s
✅ MARKDOWN	markdownlint	3		0	0.74s
✅ MARKDOWN	markdown-link-check	4		0	9.58s
✅ MARKDOWN	markdown-table-formatter	4		0	0.22s
✅ REPOSITORY	checkov	yes		no	10.68s
✅ REPOSITORY	gitleaks	yes		no	0.23s
✅ REPOSITORY	git_diff	yes		no	0.02s
✅ REPOSITORY	grype	yes		no	15.8s
✅ REPOSITORY	secretlint	yes		no	0.81s
✅ REPOSITORY	trivy	yes		no	10.46s
✅ REPOSITORY	trivy-sbom	yes		no	0.15s
✅ REPOSITORY	trufflehog	yes		no	4.36s
✅ YAML	prettier	11		0	0.61s
✅ YAML	v8r	11		0	11.92s
✅ YAML	yamllint	11		0	0.33s

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