Silence PytestUnknownMarkWarning by setting marker for pytest-benchmark (#2912)

Registering custom marker for pytest-benchmark in pyproject.toml, following https://docs.pytest.org/en/7.4.x/example/markers.html#registering-markers.

Author: weiji14

pyproject.toml

@@ -160,3 +160,6 @@ max-args=10
 [tool.pytest.ini_options]
 minversion = "6.0"
 addopts = "--verbose --durations=0 --durations-min=0.2 --doctest-modules --mpl --mpl-results-path=results"
+markers = [
+    "benchmark: mark a test with custom benchmark settings.",
+]