[BUG][swift5] Missing minimum xcode supported version

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• Have you provided a full/minimal spec to reproduce the issue?
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Description

Hi,

I ran into an issue with the swift generator, which generated code did not compile.
In the end, it got solved by a simple xcode upgrade (so, to be clear, every thing works fine on the last xcode).

As I did not saw anything about a minimum supported swift version (did I missed it ?) and the errors were very obscure, I thought I would post an issue as it could eventually help others.

Could it be possible to document the minimum versions somewhere ? Or even add it as a requirement of the swift package (I think I saw it was possible but I must admit that I am still a swift newcomer) ?

I actually got 2 errors.
The first one was about a type that could not be used with `any` (something allowed in recent versions of swift)
The second one was about `URLSession` not implementing all functions of `URLSessionProtocol`

That second one is pretty interesting, as it turns out it is due to the `@Sendable`.
At some point in swift's life, the `@Sendable` decorator has been added to the `dataTask` method of `URLSession`.
The `URLSessionProtocol` did not had this decorator, but xcode compiler was able to figure out that the functions were the same and just issued a warning about the missing `@Sendable`.
The warning has been solved by this commit (https://github.com/OpenAPITools/openapi-generator/pull/13906/commits/a9f29a08b9314a7a8fb0534ad554c056b374d412).
But it turns out that, if the new code is used with an older version of xcode/the lib, the compiler considers the `dataTask` function to be different from the one with the `@Sendable` decorator and therefore, ask for the missing implementation of the function without it.

Strangely, the apple's documentation says nothing about a change in this function.

openapi-generator version

6.0.1

Not exactly a regression

OpenAPI declaration file content or url

Not linked to the input file.

Generation Details

Simple generation in swift5
openapi-generator generate -i agent/doc/api.json -g swift5 -o generated

Steps to reproduce

Just try to compile the swift5 code using an "old" xcode.
I forgot the exact version of xcode I was using, but digging through the changelog, I would say any version prior to xcode 14.0 (12/09/2022)

Related issues/PRs

Did not found any similar issues

Suggest a fix

Maybe just a bit of documentation, or eventually some settings within the swift package to inform the compiler of the minimum required versions if that exists.

Start with the swift5 generator and the generated package produced by openapi-generator generate -i agent/doc/api.json -g swift5 -o generated; inspect how its Swift package requirements are declared. Compare compilation on the pre-Xcode 14 versions described in the issue, then document the minimum supported Xcode/Swift versions or add the appropriate package requirement, with a reproducible verification.