python38Packages.httplib2: resurrect

Without this patch, this is what happened:

```sh
➤ nix-build -A python38Packages.httplib2
error: flask-sqlalchemy-3.0.3 not supported for interpreter python3.8
(use '--show-trace' to show detailed location information)
```

That missing dependency was just for testing, but it doesn't make much sense to remove a package just because it can't be tested.

I just changed it so that it only runs checks when running at python >= 3.9, and now httplib2 is available for Python 3.8 again.

pkgs/development/python-modules/httplib2/default.nix

@@ -10,6 +10,7 @@
 , pytest-randomly
 , pytest-timeout
 , pytestCheckHook
+, pythonAtLeast
 , six
 }:
 
@@ -39,8 +40,8 @@ buildPythonPackage rec {
     pytestCheckHook
   ];
 
-  # Don't run tests for Python 2.7
-  doCheck = !isPy27;
+  # Don't run tests for older Pythons
+  doCheck = pythonAtLeast "3.9";
 
   postPatch = ''
     sed -i "/--cov/d" setup.cfg