Externals Update, main branch (2024.10.14.)

Updated all projects to atlasexternals-2.1.26. The changes wrt. atlasexternals-2.1.25 are (atlasexternals@2.1.25...2.1.26):

• Updated Acts to version 37.0.1 (not strictly relevant, as we use this version already through the build_externals.sh overrides);
• Updated Geant4 to version 10.6.3.14 (thanks to @bmorgan, meant for ATLASSIM-7265);
• Introduced nanobind 2.1.0 into AnalysisBaseExternals and AthAnalysisExternals.

Pinging @gwatts, @krumnack and @feickert for the nanobind addition.

I don't expect complications (having done a local AthSimulation build myself), but because of the G4 update let's do a detailed test in the CI. 🤔