pytest_plugin: Fix mypy error and use FixtureRequest public import
(swh) ✔ ~/swh/swh-environment/swh-core [master|⚑ 4]
13:47 $ pre-commit run -a mypy
mypy.....................................................................Failed
- hook id: mypy
- exit code: 1
swh/core/pytest_plugin.py:138: error: "FixtureRequest" has no attribute "fspath"; maybe "path"?
Found 1 error in 1 file (checked 54 source files)
Migrated from D7512 (view on Phabricator)