Fix: Go isn't detected as installed in ensure-genmanifest

The fact that 1.16 != "1.16" meant Go was reinstalled on every call to
ensure-genmanifest. This CL fixes this issue.

Change-Id: Ia3d49f03218da32379620e92d26e15d22cdc5521
diff --git a/roles/ensure-genmanifest/tasks/main.yaml b/roles/ensure-genmanifest/tasks/main.yaml
index 2732814..7ff69f6 100644
--- a/roles/ensure-genmanifest/tasks/main.yaml
+++ b/roles/ensure-genmanifest/tasks/main.yaml
@@ -2,7 +2,7 @@
   include_role:
     name: ensure-go
   vars:
-    go_version: 1.16
+    go_version: "1.16"
 - name: Install genmanifest
   include_role:
     name: go