Bump sigstore from 3.6.5 to 4.2.0

Bumps [sigstore](https://github.com/sigstore/sigstore-python) from 3.6.5 to 4.2.0.
- [Release notes](https://github.com/sigstore/sigstore-python/releases)
- [Changelog](https://github.com/sigstore/sigstore-python/blob/main/CHANGELOG.md)
- [Commits](sigstore/sigstore-python@v3.6.5...v4.2.0)

---
updated-dependencies:
- dependency-name: sigstore
  dependency-version: 4.2.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

mypy-requirements.txt

@@ -5,6 +5,6 @@ pyfakefs
 pytest
 pytest-mock
 python-gnupg  # untyped :(
-sigstore==3.6.5
+sigstore==4.2.0
 types-paramiko
 types-requests