#24527 Update go-server deps

to close https://github.com/OpenAPITools/openapi-generator/pull/24058/

PR checklist

• 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.
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Summary by cubic

Raise Go server template, samples, CI, and tests to Go 1.25 and github.com/go-chi/chi/v5 v5.2.4. Previously these used Go 1.18 and chi v5.2.2; generated servers now target Go 1.25 and chi v5.2.4.

• Changes

  • Template go.mod.mustache: go 1.18 → 1.25; github.com/go-chi/chi/v5 v5.2.2 → v5.2.4.
  • Sample go.mod: set go 1.25; chi-based samples pin github.com/go-chi/chi/v5 v5.2.4.
  • CI samples workflow uses Go 1.25.
  • Sample test updated to expect go 1.25.

• Migration

  • Build and test with Go 1.25+.
  • Regenerate Go servers and run go mod tidy.

cc @antihax (2017/11) @grokify (2018/07) @kemokemo (2018/09) @jirikuncar (2021/01) @ph4r5h4d (2021/04) @lwj5 (2023/04)