python-packages: SQLAlchemy: skip tests on Py3k

They would fail anyway, blocking all dependents for the sake of
a mere test dependency.

pkgs/top-level/python-packages.nix

@@ -11909,10 +11909,14 @@ let
       md5 = "470ca4da4a0081efc830f0d90dd91682";
     };
 
-    buildInputs = with self; [ nose mock ];
-
+    buildInputs = with self; [ nose mock ]
+      ++ stdenv.lib.optional doCheck pysqlite;
     propagatedBuildInputs = with self; [ modules.sqlite3 ];
 
+    # Test-only dependency pysqlite doesn't build on Python 3. This isn't an
+    # acceptable reason to make all dependents unavailable on Python 3 as well
+    doCheck = !isPy3k;
+
     checkPhase = ''
       ${python.executable} sqla_nose.py
     '';