* Update Github workflows
  PR: https://github.com/aibasel/downward/pull/314/changes

* Update website
  PR: https://github.com/aibasel/downward-markdown/pull/11/changes

Thank you. I handled the comments and merged both PRs.

Thanks! I reviewed both pull requests, but only had comments for one of them.
If you're happy with it, feel free to merge after you've had a look at the comments.

One of the workarounds was not specific to Ubuntu 22.04 so I reintroduced it with an updated comment. I also had to disable Wzero-as-null-pointer-constant in one line of the code that compared to pairs as GCC 16 generates a spurious warning there. I also added a companion PR for the changes to the downward-markdown repository: https://github.com/aibasel/downward-markdown/pull/11/changes

I prepared a pull request: https://github.com/aibasel/downward/pull/314

The new clang versions found a bug in an assertion of SoPlex that the previous versions and GCC ignored. Upgrading the SoPlex version from 7.1.0 to 7.1.2 fixes this. In fact, we were already inconsistent and used 7.1.0 in some places and 7.1.1 in others. Now the container templates, the README, the build instructions, and the Github workflows consistently use 7.1.2. I intentionally did not change it in CMakeLists.txt because that would break gcc builds for people who currently have 7.1.0 installed.

Other than that, I was able to remove two special cases in the workflow which we had to work around issues with Ubuntu 22.04. The build actions are all green.

The pull request is ready for review. Does this need experiments, or should we just merge?

Since the release of Ubuntu 26.04, we should now change what versions of Ubuntu, GCC, Clang, and Python we test on.

From https://www.fast-downward.org/26.6/for-developers/requirements/
> Python: we test the default Python version of the two latest Ubuntu LTS
> releases.
> 
> GCC and Clang on Ubuntu: the latest GCC and Clang versions available via apt 
> on the latest two Ubuntu LTS releases and the default GCC version in the 
> latest Ubuntu LTS release.

Python:
  Default on Ubuntu 24.04: 3.12
  Default on Ubuntu 26.04: 3.14

GCC:
  Latest apt-installable version on Ubuntu 24.04: 14
  Default on Ubuntu 26.04: 15

Clang:
  Latest apt-installable version on Ubuntu 24.04: 20
  Default on Ubuntu 26.04: 21