set a lower bound of pytest-benchmark that supports Python 3.8

Author: skshetry

pyproject.toml

@@ -29,7 +29,7 @@ Homepage = "https://github.com/fsspec/ossfs"
 [project.optional-dependencies]
 tests = [
     "aliyun-python-sdk-sts==3.1.2",
-    "pytest-benchmark>=5,<6",
+    "pytest-benchmark>=4,<6",
     "pytest-cov>=3,<6",
     "pytest-mock>=3.8.2,<4",
     "pytest>=7.2.0,<8",