Bump `k8s-openapi` to 0.23 for Kubernetes 1.31 support

[clux]

Bumps to k8s-openapi 0.23 for Kubernetes v1_31 support. As per policy, also bumps MK8SV to 1.26.

Note:

• minor internal change in client_ext due to the type change in LocalObjectReference: before / after.
• removal of 1.25 gate as 1.26 is MSRV so Ephemeral containers are GA for us
• cargo-msrv has some issues with new workspace layout - local check run gave a bump to 1.77.2 so have committed that

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 75.3%. Comparing base (6118818) to head (f51471f). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1581 +/- ## ===================================== Coverage 75.3% 75.3% ===================================== Files 82 82 Lines 7331 7331 ===================================== Hits 5519 5519 Misses 1812 1812 ``` | [Files with missing lines](https://app.codecov.io/gh/kube-rs/kube/pull/1581?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=kube-rs) | Coverage Δ | | |---|---|---| | [kube-client/src/api/mod.rs](https://app.codecov.io/gh/kube-rs/kube/pull/1581?src=pr&el=tree&filepath=kube-client%2Fsrc%2Fapi%2Fmod.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=kube-rs#diff-a3ViZS1jbGllbnQvc3JjL2FwaS9tb2QucnM=) | `68.1% <ø> (ø)` | | | [kube-client/src/client/client\_ext.rs](https://app.codecov.io/gh/kube-rs/kube/pull/1581?src=pr&el=tree&filepath=kube-client%2Fsrc%2Fclient%2Fclient_ext.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=kube-rs#diff-a3ViZS1jbGllbnQvc3JjL2NsaWVudC9jbGllbnRfZXh0LnJz) | `84.5% <100.0%> (ø)` | |