CI: Update to GCC 14 and Clang 20

[trflynn89]

[ADKaster]

Your clang docs changes seems to bump the minimum clang version to 20. We can probably keep that at 18 or 19

[trflynn89]

hmm my intent was to have the docs strongly suggest using the same compiler version we use in CI, but have the build continue with an older "known good" version. Which is how it should behave via find_compiler.sh.

The only places that mention a minimum version in the docs are CLionConfiguration.md and the Custom CMake build directory section of BuildInstructionsLadybird.md. I'd think I'd actually rather them not mention specific versions at all, and instead just link to the recommended versions in the installation steps.

[github-actions[bot]]

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[trflynn89]

I've pushed what that looks like. We now mentioned recommended and minimum compilers in the "Build Prerequisites" section of BuildInstructionsLadybird.md. Other docs now link to that section.