add action to create pr in other repos if this repo has a new version

[ahms5]

Changes proposed in this pull request:

• this action is triggerd by add template to sent trigger version #50
• it will be executed in each repo and will automatically update create new Prs on new versions.
• it was manually tested by
  • setup action to test it: CI: action to create PR on template update  spharpy#320
  • the resulting pr: [Bot]: apply copier template version v0.1.0 spharpy#321
  • those prs were closed again as they were just for testing

[Copilot]

Pull request overview

This PR adds a new GitHub Actions workflow to downstream template-generated repositories so that, when a new template version is announced via repository_dispatch, each repo can automatically run copier update and open a draft PR with the updates.

Changes:

• Add a new workflow template (create_pr_on_template_updates) that runs on repository_dispatch and opens a PR with peter-evans/create-pull-request.
• Extend copier template tests to assert the workflow file is generated and contains the expected Python version.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
tests/test_copier.py	Adds assertions that the new workflow is generated and includes the expected python-version.
template/.github/workflows/create_pr_on_template_updates.yml.jinja	Introduces the new workflow that applies Copier updates and creates a draft PR on new template version dispatch events.

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