[BUG] [Python][Template] client default headers override explicitly passed headers

[RonnyPfannschmidt]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

openapi-generator/modules/openapi-generator/src/main/resources/python/api_client.mustache

Lines 137 to 139 in b9e7595

	# header parameters
	header_params = header_params or {}
	header_params.update(self.default_headers)

this piece of code ensures that the given parameters for a call always override the rest
i believe it should start with a copy of the defaults and update with the given parameters

but i'd like to get upstream confirmation

openapi-generator version

all i'm aware of (4.x.y, 5.x.y)

OpenAPI declaration file content or url

not needed yet

Generation Details

not needed yet

Steps to reproduce

1. create a client object with some default headers
2. call the api with a override to the headers
3. observe the overrides being replaced with the defaults

Related issues/PRs

haven't found any

Suggest a fix

based on upstream response i'll either contribute a fix or change the way we call the code in our project

[spacether]

@RonnyPfannschmidt our handling of headers can definitely be improved.
Yes, we should definitely start with the default and then override with user provided.
Looking forward to any improvements on this.