Clean up warning catching in pytest.ini (#10438)

Several of these have been fixed, so let's update the requirement if
necessary and remove the warning catching.

`python-dateutil 2.9.0` was released Feb 29, 2024, so it's not widely
packaged in non-EOL major distros yet.
`pytest-cov 4.1.0` was released May 24, 2023.
Our pinned versions were already higher than these requirements.

Alternatively, we could just remove the warnings and not update the
minimum requirement, but I think it's nicer to note it in requirements
for anyone running our tests, like packagers.

We already require `poetry-plugin-export>=1.9.0`. `1.7.0` updated its
`requests-toolbelt` requirement to `>=1.0.0`, which is greater than the
minimum version needed to remove the warning.

certbot/pyproject.toml

@@ -58,7 +58,7 @@ test = [
     "pip",
     "pylint",
     "pytest",
-    "pytest-cov",
+    "pytest-cov>=4.1.0", # https://github.com/pytest-dev/pytest-cov/pull/558
     "pytest-xdist",
     "ruff",
     "setuptools",