Fix singular and plural for 'findings'

[hugovk]

Fix "1 findings" -> "1 finding" and keep "2 findings".

Before

❯ zizmor .
🌈 completed main.yml
🌈 completed deploy.yml
🌈 completed lint.yml
warning[artipacked]: credential persistence through GitHub Actions artifacts
  --> /Users/hugo/github/cherry-picker/.github/workflows/lint.yml:16:9
   |
16 |       - uses: actions/checkout@v4
   |         ------------------------- does not set persist-credentials: false
   |
   = note: audit confidence → Low

1 findings: 0 unknown, 0 informational, 0 low, 1 medium, 0 high

After

❯ /tmp/zizmor/target/debug/zizmor .
🌈 completed lint.yml
🌈 completed main.yml
🌈 completed deploy.yml
warning[artipacked]: credential persistence through GitHub Actions artifacts
  --> /Users/hugo/github/cherry-picker/.github/workflows/lint.yml:16:9
   |
16 |       - uses: actions/checkout@v4
   |         ------------------------- does not set persist-credentials: false
   |
   = note: audit confidence → Low

1 finding: 0 unknown, 0 informational, 0 low, 1 medium, 0 high

[woodruffw]

Thanks @hugovk!