Fix Anaconda environment configuration for tests (#40)

In order to fix #38, we need to hard
pin the version of Werkzeug used by Flask to avoid the changes after
to how functions are organized in the library's modules.

See PR Sanster/IOPaint#390 with a related solution (not specific to
Anaconda approach, but informative).

See [StackOverflow](https://stackoverflow.com/a/77217971) post for
details.

environment.yml

@@ -38,3 +38,4 @@ dependencies:
     - jsonschema==4.17.3
     - jwcrypto==1.5.0
     - PyJWT==2.8.0
+    - werkzeug==2.2.2