Ignore the two dependabot updates that cannot land yet

[royalpinto007]

Why

Two dependabot updates cannot land and are re-proposed every week, failing at
npm ci each time. That is noise, and worse, it trains everyone to ignore a red
dependabot PR.

• @opennextjs/cloudflare needs Next 15 (Migrate to Next 15 so the Cloudflare adapter can move again #89)
• @vitejs/plugin-react needs vite 8 via vitest (Move vitest onto vite 8 so @vitejs/plugin-react can update #90)

Scope

Add ignores to .github/dependabot.yml so these stop until the blocking
migration happens, with the reason and the issue in a comment so the ignore does
not become permanent by accident:

    ignore:
      # Needs Next 15: 1.15.1 is the last release accepting next 14. See #89.
      - dependency-name: "@opennextjs/cloudflare"
      # Needs vite 8, which means moving vitest first. See #90.
      - dependency-name: "@vitejs/plugin-react"

Done when

• Both entries are present with a comment naming the blocking issue
• The next dependabot run does not re-open either PR
• Migrate to Next 15 so the Cloudflare adapter can move again #89 and Move vitest onto vite 8 so @vitejs/plugin-react can update #90 each carry a line saying to remove the ignore as part of the work

Good first issue

Yes. It is a config edit, but read #89 and #90 first so the comments say
something true.