requirements: Unpin tblib

Shouldn't have merged the pyup bot proposed change.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

requirements-test.txt

@@ -2,5 +2,5 @@ mysqlclient~=2.1.0
 psycopg2-binary~=2.9.0
 sqlparse~=0.4.0
 python-dateutil~=2.8.0
-tblib==2.0.0
+tblib~=2.0.0
 openapi-core~=0.16.4