test: cover anonymous security alternatives

[kriptoburak]

Summary

• Add a ruleset regression test for operation security lists that include an anonymous alternative.
• Keep the existing scheme usage valid while covering the empty security requirement object from OpenAPI.

Validation

• git diff --check
• node --check packages/ruleset/test/rules/securityschemes.test.js
• Not run: npm ci or npm run test-ruleset because this clone has no node_modules and local disk is nearly full.

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