update normalizer doc with correct path to spec

[wing328]

a follow up pr to #23543

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• 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.
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Summary by cubic

Updated the OpenAPI normalizer example to use the java generator and the correct spec path, and added a short diff showing the schema changes from REPLACE_ONE_OF_BY_DISCRIMINATOR_MAPPING. This avoids path errors and clarifies the normalizer’s effect.

^{Written for commit d7ebcfe. Summary will update on new commits. Review in cubic}