Add pytest-mock to meta.yaml test req

[lrandersson]

Description

This PR intends to resolve the test failure on the canary builds:
32f91ad
Seems like I forgot to also update the recipe test requirements to include the new package: #1228. On main the canary build is failing with the new tests:

 ERROR tests/test_fcp.py::test_check_duplicates_files_returns_max_path_length
 ERROR tests/test_fcp.py::test_check_duplicates_files_empty_packages
 ERROR tests/test_fcp.py::test_check_duplicates_files_with_env_prefixes
 ERROR tests/test_fcp.py::test_check_duplicates_files_env_prefix_normalizes_trailing_slash

In particular:

E       fixture 'mocker' not found

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?