Fix staticcheck ST1005 errors in generated Go client

[maelick]

Fixes #13632 by updating the mustache templates that did not follow ST1005.
Verification can be done by rerunning client generation and staticcheck.

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Tagging Go technical committee: @antihax @grokify @kemokemo @jirikuncar @ph4r5h4d

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[wing328]

CI failed: https://app.circleci.com/pipelines/github/OpenAPITools/openapi-generator/19997/workflows/49162131-d99f-4575-8c15-776f0f253eda/jobs/51187

I think you may need to update the tests as well, which may compare the error messages.

[maelick]

Fixed