#25390 ci: set SBT version to 1.10.11 for scala pekko

PR checklist

The pekko sample generation does not pin its sbt version, which leads to it being resolved to v2, which required JDK 17. The pipeline uses JDK 11. Spotted as an issue in https://github.com/OpenAPITools/openapi-generator/pull/25383.

I have updated the samples to mimic what exists for akka, where the version is pinned to 1.x.

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.