fix https://github.com/Blazemeter/taurus/issues/1947: deduplicate in included-configs

[wuxudong]

fix duplicated requests introduced by cascade included-configs

Each PR must conform to Developer's Guide.

Quick checklist:

• Description of PR explains the context of change
• Unit tests cover the change, no broken tests
• No static analysis warnings (Codacy etc.)
• Documentation update ('available in the unstable snapshot' warning if necessary)
• Changes file inside site/dat/docs/changes directory, one-line note of change inside

[wuxudong]

@henrychv
For pull requests, only main branch not master can trigger test and codecov because of following code in .github/workflows/ci.yaml

name: CI

on:
  push:
  pull_request:
    branches: [main]