Unbreak unit tests by updating .fixtures.yml

The unit tests started failing after stdlib 9.0.0 was made a requirement. Fix
this by updating the unit test dependencies.

URL: #54

.fixtures.yml

@@ -1,9 +1,11 @@
 fixtures:
   forge_modules:
-    stdlib: "puppetlabs/stdlib"
+    stdlib:
+      repo: "puppetlabs/stdlib"
+      ref: "9.4.1"
     cron_core:
       repo: "puppetlabs/cron_core"
-      ref: "1.0.0"
+      ref: "1.2.1"
       puppet_version: ">= 7.0.0"
     k5login_core:
       repo: "puppetlabs/k5login_core"