Upgrade Ubuntu in CI (and pin oscrypto to an unreleased bugfix)

[nolar]

Ubuntu 24.04 is blocked by wbond/oscrypto#78:

____________ ERROR collecting tests/admission/test_certificates.py _____________
tests/admission/test_certificates.py:1: in <module>
    import certvalidator
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/certvalidator/__init__.py:9: in <module>
    from .validate import validate_path, validate_tls_hostname, validate_usage
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/certvalidator/validate.py:5: in <module>
    from oscrypto import asymmetric
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/asymmetric.py:19: in <module>
    from ._asymmetric import _unwrap_private_key_info
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/_asymmetric.py:[27](https://github.com/nolar/kopf/actions/runs/11899842142/job/33159360248#step:6:28): in <module>
    from .kdf import pbkdf1, pbkdf2, pkcs12_kdf
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/kdf.py:9: in <module>
    from .util import rand_bytes
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/util.py:14: in <module>
    from ._openssl.util import rand_bytes
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/_openssl/util.py:6: in <module>
    from ._libcrypto import libcrypto, libcrypto_version_info, handle_openssl_error
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/_openssl/_libcrypto.py:15: in <module>
    from ._libcrypto_ctypes import (
/opt/hostedtoolcache/Python/3.13.0/x64/lib/python3.13/site-packages/oscrypto/_openssl/_libcrypto_ctypes.py:47: in <module>
    raise LibraryNotFoundError('Error detecting the version of libcrypto')
E   oscrypto.errors.LibraryNotFoundError: Error detecting the version of libcrypto