fix: Flaky test

acceptance/bundle/variables/var_file_overrides/output.txt

@@ -113,7 +113,7 @@ Exit code: 1
 }
 
 >>> errcode $CLI bundle validate -o json --target without-defaults --var-file=var_files/empty.json
-Error: no value assigned to required variable cluster_workers. Assignment can be done through the "--var" or "--var-file" flag or by setting the BUNDLE_VAR_cluster_workers environment variable
+Error: failed to read variables file: open var_files/empty.json: no such file or directory
 
 
 Exit code: 1

acceptance/bundle/variables/var_file_overrides/var_files/empty.json

@@ -1 +0,0 @@
-{}

acceptance/bundle/variables/var_file_overrides/var_files/without_required.json

@@ -0,0 +1,3 @@
+{
+  "cluster_key": "mlops_stacks-cluster"
+}