runtime/sam: fix IN with union first operand (#6662)

Author: nwt

runtime/sam/expr/eval.go

@@ -134,7 +134,7 @@ func NewIn(sctx *super.Context, elem, container Evaluator) *In {
 }
 
 func (i *In) Eval(this super.Value) super.Value {
-	elem := i.elem.Eval(this)
+	elem := i.elem.Eval(this).Deunion()
 	if elem.IsError() {
 		return elem
 	}

runtime/ztests/expr/in.yaml

@@ -41,6 +41,27 @@ output: |
 
 ---
 
+spq: |
+  values this in [1,2::(int64|null),null,error(0)]
+
+vector: true
+
+input: |
+  1::(int64|null)
+  2
+  null
+  null::(int64|null)
+  error(0)
+
+output: |
+  true
+  true
+  null
+  null
+  error(0)
+
+---
+
 # Test in expressions on a map constant.
 spq: |
   const m = |{"a":1,"b":2}|