Re-enable multiple gerrit connection test

Re-enable the test with multiple gerrits affecting the same projects.
Extends the test a bit as the last test never showed actual interaction
between the two builds.

Story: 2000773
Task: 3412
Change-Id: Ia8621ea481057cc7602dd01ef149b2ebfbf0aa58
diff --git a/tests/fixtures/config/zuul-connections-multiple-gerrits/main.yaml b/tests/fixtures/config/zuul-connections-multiple-gerrits/main.yaml
new file mode 100644
index 0000000..730cc7e
--- /dev/null
+++ b/tests/fixtures/config/zuul-connections-multiple-gerrits/main.yaml
@@ -0,0 +1,6 @@
+- tenant:
+    name: tenant-one
+    source:
+      review_gerrit:
+        config-repos:
+          - common-config