python3Packages.fsspec: fix tests on linux

Hydra fails with a `DirectoryError: [Errno 21] Is a directory: '/build/source/fsspec/tests/__pycache__'`.
I suspect that both drvs `python37Packages.fsspec` and `python38Packages.fsspec` share the same folder
`'/build/source/fsspec/tests/__pycache__'` which leads to problems. To fix it I just let each drvs run in a
tmp directory using `pytestFlagsArray = [ "--rootdir=$(mktemp -d)" ];`.

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

@@ -24,13 +24,18 @@ buildPythonPackage rec {
     numpy
   ];
 
+  pytestFlagsArray = [ "--rootdir=$(mktemp -d)" ];
+
   disabledTests = [
     # Test assumes user name is part of $HOME
     # AssertionError: assert 'nixbld' in '/homeless-shelter/foo/bar'
     "test_strip_protocol_expanduser"
   ] ++ lib.optionals (stdenv.isDarwin) [
-    "test_modified" # fails on hydra, works locally
-    "test_touch" # fails on hydra, works locally
+    # works locally on APFS, fails on hydra with AssertionError comparing timestamps
+    # darwin hydra builder uses HFS+ and has only one second timestamp resolution
+    # this two tests however, assume nanosecond resolution
+    "test_modified"
+    "test_touch"
   ];
 
   meta = with lib; {