ci: rtCamp/action-slack-notify version mismatch between workflows

[Ankitsinghsisodya]

Problem

Two workflows use different versions of rtCamp/action-slack-notify:

• .github/workflows/kind-e2e.yaml line 142: @v2.1.0
• .github/workflows/weekly-office-hours-slack-reminder.yaml line 40: @v2.2.1

The inconsistency means the two workflows may have different behaviour and it makes future updates harder to track.

Proposed Fix

Standardize both to rtCamp/action-slack-notify@v2.2.1 (the higher existing version).

[Ankitsinghsisodya]

/assign