Add validation for duplicate team entries

[vivekjami]

This PR adds validation to check for duplicate entries in team members and alumni lists.

Fixes rust-lang/team #1918

Changes:

• Added new validate_duplicate_team_entries function
• Checks team members and alumni
• Uses separate function for cleaner code design as suggested by @Kivooeo

[vivekjami]

@marcoieni

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing github

[Kivooeo]

I tried open the link from #2032 (comment)

And it seems like it was disabled due to inactivity, so I updated link, so you can see https://github.com/rust-lang/team/compare/main...Kivooeo:team:add-check?expand=1, how I made this and read this comment above about some details, but I lean to this solution because it does account leads as well without repeating logic in check function

[vivekjami]

Yes @Kivooeo , I saw your pr and i agree with your approach but i do not know if i can change the schema.rs as that was not specified in the pr and that is the cleanest way to handle team leads and I want to see the errors that needs to resolve in a single check so that i can solve the issue, so that is why i avoided bail!() , if i used that then your code works perfectly. @marcoieni any thoughts?

[marcoieni]

you can change schema.rs, for sure!
Extracting the logic so that you don't repeat it, also sounds great!

[vivekjami]

@marcoieni just updated the code with the new requirements