The commit SHAs did not match their version comment tags, as
flagged by zizmor ref-version-mismatch. Update all three actions
to their latest releases with correct SHAs.

- actions/setup-python v5.0.0 -> v5.6.0
- actions/setup-java v4.0.0 -> v4.8.0
- gacts/run-and-post-run v1.4.0 -> v1.4.3

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The following errors happened at the actions/setup-python step.

https://github.com/ruby/ruby/actions/runs/18229870239

> The version '3.x' with architecture 's390x' was not found for Ubuntu 24.04.
> The list of all available versions can be found here: https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json

> The version '3.x' with architecture 'ppc64' was not found for Ubuntu 24.04.
> The list of all available versions can be found here: https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json

After skipping the actions/setup-python step, the following errors also
happened at the actions/setup-java step.

https://github.com/ruby/ruby/actions/runs/18355975425?pr=14721

> make-ibm (check, ubuntu-24.04-ppc64le)
> Could not find satisfied version for SemVer '17'.

> make-ibm (check, ubuntu-24.04-s390x)
> The process '/usr/bin/bash' failed with exit code 1

> make-ibm (check, ubuntu-24.04-s390x)
> Process completed with exit code 127.

To fix the errors, I started using the Java distribution semeru (IBM Semeru
Runtime Open Edition) on the ppc64le/s390x cases.

You can see the following page for the details of the Java distribution semeru.

https://github.com/actions/setup-java?tab=readme-ov-file#supported-distributions
https://github.com/actions/setup-java/blob/ead9eaa3cfe0b0fc2fa749519ae09c3d4f4080b0/src/distributions/semeru/installer.ts#L20-L27

I've enabled the [Predictive Test Selection](https://www.launchableinc.com/docs/features/predictive-test-selection/) feature, which let machine-learning model selects the appropriate tests to reduce CI execution time in https://github.com/ruby/ruby/pull/12617.

However, I noticed that there are some problems for enabling PTS in Ruby CI after several experiments. Until fixing the problem, I'll disable this feature by removing `launchable subset` command.

As well as compilers/entrypoint.sh.