Improve banned users filter for issues queries

What does this MR do and why?

Adds a +0 to the author_id clause to prevent a bad query plan flip.

Example queries

1. Project issue list

   • gitlab-org/gitlab (bad plan before)
     • Before: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119414
     • After: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119416
   • issue-reproduce/issue-reproduce (already using nested loop before)
     • Before: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119421
     • After: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119423

2. Project issue exists

• Before: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119424
• After: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119425

3. Group issue list (no difference, already using nested loop)

• Before: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119432
• After: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/38726/commands/119434

References

Related to #394980 (closed)

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