[python][template] move _path_to_item of simple init to avoid name error

[RonnyPfannschmidt]

fixes #8736

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[RonnyPfannschmidt]

tech committee ping: @taxpon (2017/07) @frol (2017/07) @mbohlool (2017/07) @cbornet (2017/09) @kenjones-cisco (2017/11) @tomplus (2018/10) @Jyhess (2019/01) @arun-nalla (2019/11) @spacether (2019/11)

[spacether]

Looks good, thanks!

[wing328]

@RonnyPfannschmidt thanks for the PR, which has been included in the v5.1.0 release: https://twitter.com/oas_generator/status/1373636654024380423