Bump pikepdf from 8.11.2 to 8.12.0 in /docker/readpdf

Bumps [pikepdf](https://github.com/pikepdf/pikepdf) from 8.11.2 to 8.12.0.
- [Release notes](https://github.com/pikepdf/pikepdf/releases)
- [Commits](pikepdf/pikepdf@v8.11.2...v8.12.0)

---
updated-dependencies:
- dependency-name: pikepdf
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>