Mock server in WFS provider tests (#1534)

* Mock server in WFS provider tests

This commit mocks the layer in WFS tests and prepares return values
required to satisfy the tests. This reduces the test fidelity, but it
makes them stable and increases execution speed (literally 100x on my
machine, 66 sec to 0.6 sec).

Since the return value is mocked, it doesn't make sense to send
different parameters to the server, so some tests became obsolete.

The original tests are still there in another file, but are not supposed
to be run in CI.

* Mention wfs live tests in github CI

* Comment test file where all tests are skipped

pytest considers this to be a failure, but we still want the test file
to be mentioned here

.github/workflows/main.yml

@@ -148,6 +148,7 @@ jobs:
         pytest tests/test_ogr_shapefile_provider.py
         pytest tests/test_ogr_sqlite_provider.py
         pytest tests/test_ogr_wfs_provider.py
+        # pytest tests/test_ogr_wfs_provider_live.py  # NOTE: these are skipped in the file but listed here for completeness
         pytest tests/test_openapi.py
         pytest tests/test_oracle_provider.py
         pytest tests/test_postgresql_provider.py