chore: Add CocoaPods podspec lint CI

[marandaneto]

💡 Motivation and Context

Add CI coverage for CocoaPods package validation so podspec issues are caught automatically before release.

💚 How did you test it?

Not run successfully locally; pod lib lint PostHog.podspec --allow-warnings --skip-tests is blocked on this machine by missing Xcode 26.5 simulator/platform runtimes.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file

[greptile-apps]

_{Reviews (1): Last reviewed commit: "chore: add CocoaPods podspec lint CI" | Re-trigger Greptile}