This tiny PR fixes the spelling of an identifier that was incorrectly cased in a mustache template. The fix only affects a comment in the output, so it will make no runtime difference when consuming a generated client.

In the Python generator, the package name is available as {{packageName}}, but in src/main/resources/python/__init__apis.mustache, it was being referenced as {{packagename}}.
This produced incorrect output such as:

# In order to avoid this, import only the API that you directly need like:
#
#   from .api.my_api import MyApi

(note the missing package name)

The corrected output:

# In order to avoid this, import only the API that you directly need like:
#
#   from my_package.api.my_api import MyApi

cc @cliffano @zlx @autopp

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 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
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