Add test for passing --var twice for the same arg (#2176)

This shows that passing two --var for the same arg is rejected
currently.

acceptance/bundle/variables/arg-repeat/databricks.yml

@@ -0,0 +1,6 @@
+bundle:
+  name: arg-repeat
+
+variables:
+  a:
+    default: hello

acceptance/bundle/variables/arg-repeat/output.txt

@@ -0,0 +1,20 @@
+
+>>> errcode $CLI bundle validate --var a=one -o json
+
+Exit code: 0
+{
+  "a": {
+    "default": "hello",
+    "value": "one"
+  }
+}
+
+>>> errcode $CLI bundle validate --var a=one --var a=two
+Error: failed to assign two to a: variable has already been assigned value: one
+
+Name: arg-repeat
+Target: default
+
+Found 1 error
+
+Exit code: 1

acceptance/bundle/variables/arg-repeat/script

@@ -0,0 +1,2 @@
+trace errcode $CLI bundle validate --var a=one -o json | jq .variables
+trace errcode $CLI bundle validate --var a=one --var a=two