[BUG][Go][Server] Remove Duplicate Imports

Bug Report Checklist

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

openapi: 3.0.0
info:
  description: >-
    Test to replicate duplicate os imports.
  version: 1.0.0
  title: Duplicate Imports
  license:
    name: Apache-2.0
    url: 'https://www.apache.org/licenses/LICENSE-2.0.html'
paths:
  /file1:
    post:
      tags:
        - file1
      summary: uploads an image
      description: ''
      operationId: postFile1
      responses:
        '200':
          description: successful operation
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                additionalMetadata:
                  description: Additional data to pass to server
                  type: string
                file:
                  description: file to upload
                  type: string
                  format: binary
  /file2:
    post:
      tags:
        - file2
      summary: uploads an image
      description: ''
      operationId: postFile2
      responses:
        '200':
          description: successful operation
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                additionalMetadata:
                  description: Additional data to pass to server
                  type: string
                file:
                  description: file to upload
                  type: string
                  format: binary

• 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?

Expected Output:

package openapi

import (
	"context"
	"net/http"
	"os"
)

Actual Output:

package openapi

import (
	"context"
	"net/http"
	"os"
	"os"
)

• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

While trying to create a PR for a separate issue, I discovered that go-server (and potentially some of the other go generators have an issue with postProcessOperationsWithModels. This method can create duplicate import mappings in go-server's api.go if two separate tags try and create the same mapping.

openapi-generator version

Tried on 6.0.0-SNAPSHOT. It doesn't appear to be a regression.

OpenAPI declaration file content or url

Yaml posted above.

Generation Details

Steps to reproduce

./run-in-docker.sh java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate --input-spec test.yaml --generator-name go-server --output generated

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/3847

Suggest a fix

Trying to figure out a fix for this right now as I'm about to create a PR that makes the issue more obvious. I don't think postProcessOperationsWithModels is necessarily the problem but I'm not sure where else the imports could be added.

Run the provided run-in-docker.sh generation command with the YAML reproduction, then trace go-server's postProcessOperationsWithModels and the import mappings it produces. Done means the generated api.go contains each import only once, matching the expected output shown in the issue.