Bump pikepdf from 5.1.0 to 5.1.1

Bumps [pikepdf](https://github.com/pikepdf/pikepdf) from 5.1.0 to 5.1.1.
- [Release notes](https://github.com/pikepdf/pikepdf/releases)
- [Changelog](https://github.com/pikepdf/pikepdf/blob/master/docs/release_notes.rst)
- [Commits](https://github.com/pikepdf/pikepdf/compare/v5.1.0...v5.1.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -61,7 +61,7 @@ ocrmypdf==13.4.1
 packaging==21.3; python_version >= '3.6'
 pathvalidate==2.5.0
 pdfminer.six==20211012
-pikepdf==5.1.0
+pikepdf==5.1.1
 pillow==9.0.1
 pluggy==1.0.0; python_version >= '3.6'
 portalocker==2.4.0; python_version >= '3'