Mark x/networking-fortinet tempest plugins inactive

No changes are merging in x/networking-fortinet tempest
plugins for past 3 years so marking it inactive

- https://review.opendev.org/q/project:x%252Fnetworking-fortinet

Change-Id: I1eb9d442bd5c0644e02491b838c75fda80234434
diff --git a/tools/generate-tempest-plugins-list.py b/tools/generate-tempest-plugins-list.py
index b96bbe4..0b6b342 100644
--- a/tools/generate-tempest-plugins-list.py
+++ b/tools/generate-tempest-plugins-list.py
@@ -77,6 +77,9 @@
     'x/ranger-tempest-plugin'
     'x/tap-as-a-service-tempest-plugin'
     'x/trio2o'
+    # No changes are merging in this
+    # https://review.opendev.org/q/project:x%252Fnetworking-fortinet
+    'x/networking-fortinet'
 ]
 
 url = 'https://review.opendev.org/projects/'