test: update git repo branch ref

bigbang/values.yaml

@@ -2,7 +2,7 @@ kubevirt:
   enabled: true
   git:
     repo: https://repo1.dso.mil/platform-one/big-bang/apps/third-party/kubevirt
-    branch: image_pull_secrets
+    branch: main
     path: chart
   flux: {}