test: cover optional security fixture

[kriptoburak]

Summary

• Add an anonymous security alternative to the petstore fixture.
• Keep analyzer coverage for collecting bearer and API key schemes when anonymous access is allowed.

Validation

• go test ./internal/analyzer -run TestAnalyzeSecuritySchemes_Petstore
• git diff --check

[giraffesyo]

@kriptoburak thanks for the PR. I only saw the testdata addition, was there a test file you meant to commit alongside it?

The generator currently only reads components.securitySchemes and operation-level security, the document-level security array this line touches isn't consumed anywhere yet.