Tests: fix requirements for unit tests

Add WebTest to test-requirements which used to be imported as a
transitive requirement via pecan, but the latest release of
pecan dropped this dependency. So make this requirement explicit,
see [1].
Add Neutron and l2gw as required project to py310 job in .zuul.yaml

[1]: https://review.opendev.org/c/openstack/neutron/+/848706
Change-Id: I02c00f46ad453c25981475ce53421827df97a717

.zuul.yaml

@@ -23,6 +23,10 @@
             required-projects:
               - openstack/neutron
               - x/networking-l2gw
+        - openstack-tox-py310:
+            required-projects:
+              - openstack/neutron
+              - x/networking-l2gw
     gate:
       jobs:
         - networking-l2gw-tempest-dummy
@@ -37,3 +41,7 @@
             required-projects:
               - openstack/neutron
               - x/networking-l2gw
+        - openstack-tox-py310:
+            required-projects:
+              - openstack/neutron
+              - x/networking-l2gw

test-requirements.txt

@@ -22,3 +22,7 @@ testresources>=2.0.0 # Apache-2.0/BSD
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT
 ddt>=1.0.1 # MIT
+
+# This is necessary as pecan dropped this dependency
+# see https://review.opendev.org/c/openstack/neutron/+/848706
+WebTest>=2.0.27 # MIT