Fix Windows CI: Use python -m pytest instead of pytest command

[Copilot]

Windows runners fail with "pytest is not recognized" error because pip-installed scripts may not be immediately available in PowerShell PATH.

Changes

• .github/workflows/CI-models.yml: Changed pytest tests/ to python -m pytest tests/ in Windows job
• .github/workflows/CI.yml: Changed pytest brainpy/ to python -m pytest brainpy/ in Windows job

Linux and macOS jobs unchanged - direct pytest invocation works correctly there.

- pytest tests/
+ python -m pytest tests/

Using python -m pytest invokes pytest as a module, bypassing PATH resolution issues on Windows.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[BUG] The windows runner raised an error when running "Continuous Integration with Models" ci</issue_title>
<issue_description>The windows runner raised an error when running "Continuous Integration with Models" ci.

pytest: D:\a\_temp\2971078e-df66-4e10-9ecc-310312453275.ps1:2
Line |
   2 |  pytest tests/
     |  ~~~~~~
     | The term 'pytest' is not recognized as a name of a cmdlet, function, script file, or executable program. Check
     | the spelling of the name, or if a path was included, verify that the path is correct and try again.
Error: Process completed with exit code 1.
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes [BUG] The windows runner raised an error when running "Continuous Integration with Models" ci #810

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