tox: Bump NEO to explicit >= 1.6.2

>= 1.6 was already using latest in 1.6 series, but >= 1.6.2 is more explicit.

Also: in 1.6.2 NEO switched from MySQL-python to mysqlclient:

    nexedi/neoppod@5f0c93f5

so we switch it too.

tox.ini

@@ -15,9 +15,9 @@ deps    =
     # latest current ZODB _4_
     ZODB4:  ZODB3 >=3.11
 
-    neo:    neoppod >= 1.6
+    neo:    neoppod >= 1.6.2
     # neo.tests also imports MySQLdb unconditionally
-    neo:    MySQL-python
+    neo:    mysqlclient
 
 
     # zeo: ZEO is already required by ZODB, but for testing utilities from ZEO we also need: