update infection template

[michalsn]

Description The --only-covered flag was removed in Infection 0.31.0, see: https://infection.github.io/guide/command-line-options.html#only-covered

Failed action as a reference: https://github.com/codeigniter4projects/website/actions/runs/16732695219/job/47364306883

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [ ] Conforms to style guide