fix: Code generated in go should have a line that matches Code generated .* DO NOT EDIT.

[jensravn]

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• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

Code generated in go should have a line that matches the following
regular expression (in Go syntax):

^// Code generated .* DO NOT EDIT\.$

Described here https://pkg.go.dev/cmd/go#hdr-Generate_Go_files_by_processing_source

This will allow other tools that parses go code to treat it as generated code.

An example of this is go's deadcode tool that have the flag -generated to indicate whether it should report on generated code. By default it will skip generated code.
https://pkg.go.dev/golang.org/x/tools/internal/cmd/deadcode