fix(prview): ignore never-dispatched check suites without check runs

[AdamMagued]

Fixes #959

Summary

• Excluded empty, never-dispatched check suites from in-progress counts and Pending section rendering
• Added unit tests validating checks stats computation with empty check suites

Verified in container sandbox.

[github-actions]

👋 Hi @AdamMagued, thanks for the pull request! A scan flagged a concern with it. Could you please take a look?

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